CVE-2021-3156 "Baron Samedit"

Easy to weaponize Gives privileged access Vulnerable in default configuration

Description

Sudo before 1.9.5p2 contains an off-by-one error that can result in a heap-based buffer overflow, which allows privilege escalation to root via “sudoedit -s” and a command-line argument that ends with a single backslash character.

Add Assessment

cdelafuente-r7 (69)

January 27, 2021 3:40pm UTC (2 years ago)•

Ratings

Attacker Value

Very High

Exploitability

Very High

Common in enterprise Easy to weaponize Gives privileged access Unauthenticated Vulnerable in default configuration

Technical Analysis

Sudo is vulnerable to a local privilege escalation that enables any local user to gain root privileges. This is due to a heap-based buffer overflow when unescaping backslashes in the command’s arguments. This vulnerable code has been introduced in July 2011. According to the advisory, legacy versions from 1.8.2 to 1.8.31p2 and stable versions from 1.9.0 to 1.9.5p1 are vulnerable in their default configurations. Note that the local user password is not required to successfully exploit this vulnerability.

The exploitation is done by invoking “sudoedit -s” command to reach the vulnerable code and do an out-of-bounds write in heap memory. The security researchers were able to exploit this vulnerability and get a shell as root using 3 different methods. One of them, which seems to be the easiest and the most reliable, is demo’ed in this video.

I couldn’t find any PoC available, but there are enough technical details in the advisory to write an exploit. It is a critical bug and sudo should be patched immediately. It is very likely a working exploit will be publicly available soon.

MadDud (10)

January 30, 2021 9:59am UTC (2 years ago)•Edited 2 years ago

Ratings

Attacker Value

Very High

Exploitability

Very High

Technical Analysis

Proof of Concept

https://github.com/lockedbyte/CVE-Exploits/tree/master/CVE-2021-3156

dorpor412 (6)

January 27, 2021 8:10am UTC (2 years ago)•Edited 2 years ago

Ratings

Attacker Value

Very High

Exploitability

Very High

Easy to weaponize Gives privileged access Vulnerable in default configuration

marshalcn (2)

January 27, 2021 6:16am UTC (2 years ago)

Ratings

Attacker Value

Low

Exploitability

Low

CVSS V3 Severity and Metrics

Data provided by the National Vulnerability Database (NVD)

Base Score:

7.8 High

Impact Score:

5.9

Exploitability Score:

1.8

Vector:

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack Vector (AV):

Local

Attack Complexity (AC):

Low

Privileges Required (PR):

Low

User Interaction (UI):

None

Scope (S):

Unchanged

Confidentiality (C):

High

Integrity (I):

High

Availability (A):

High

Metasploit Modules

exploit/linux/local/sudo_baron_samedit (https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/local/sudo_baron_samedit.rb)

Exploited in the Wild

Reported by:

mkienow-r7 indicated source as Government or Industry Alert (https://www.cisa.gov/known-exploited-vulnerabilities-catalog)

Reported: April 07, 2022 3:59am UTC (11 months ago)

gwillcox-r7 indicated source as Government or Industry Alert (https://us-cert.cisa.gov/ncas/alerts/aa22-117a)

Reported: April 27, 2022 8:01pm UTC (10 months ago)

References

Rapid7

January 27, 2021 8:56pm UTC (2 years ago)• Last updated January 27, 2021 9:31pm UTC (2 years ago)

Technical Analysis

Description

On Tuesday, January 26, 2021, the Qualys Research Team published a blog post on CVE-2021-3156, a privilege escalation vulnerability in the sudo command that enables any local user to gain root privileges without using a password, even if the user is not listed in the sudoers file. The vulnerability arises from a heap-based buffer overflow when unescaping backslashes in a supplied command’s arguments. The vulnerable code was introduced in July 2011 and affects most Linux-based operating systems. See the project maintainers’ advisory on the vulnerability for further details.

Affected Products

According to the advisory, legacy versions of sudo from 1.8.2 to 1.8.31p2 and stable versions from 1.9.0 to 1.9.5p1 are vulnerable in their default configurations. Depending on the Linux distribution, the version number might be different. Please check the Guidance section for details.

Rapid7 analysis

CVE-2021-3156 is a local privilege escalation vulnerability, which means an attacker requires existing access to a target (such as through remote code execution) in order to exploit the bug. Exploitation is achieved by invoking the sudoedit -s command to reach the vulnerable code and perform an out-of-bounds (OOB) write in heap memory. Upon successful exploitation, the attacker would gain root access, resulting in full compromise of the system.

At the time of this writing, a crash PoC is available from Qualys. Rapid7 researchers have reliably reproduced the crash using the supplied PoC. The advisory contains enough technical detail to develop the PoC into an exploit. Researchers will have to bypass any memory protections in place, though the bug allows for a great amount of control over the OOB write, reducing the burden of exploitation. It is only a matter of time before exploits begin to surface.

Guidance

Rapid7 recommends that sudo users update to version 1.9.5p2 immediately. The legacy release stream 1.8.x has not yet received a critical bug fix for CVE-2021-3156. There is no effective mitigation for this vulnerability. Patched versions are listed below.

Official maintainer:

Stable release has been patched in version 1.9.5p2: https://github.com/sudo-project/sudo/releases/tag/SUDO_1_9_5p2
Legacy release has not been patched already: https://www.sudo.ws/legacy.html

Linux distributions:

Ubuntu: https://ubuntu.com/security/CVE-2021-3156
Debian: https://security-tracker.debian.org/tracker/CVE-2021-3156
RHEL: https://access.redhat.com/security/cve/CVE-2021-3156
Fedora: https://bodhi.fedoraproject.org/updates/FEDORA-2021-2cb63d912a
Arch Linux: https://security.archlinux.org/CVE-2021-3156
Gentoo: https://security.gentoo.org/glsa/202101-33

Very High