CVE-2021-3156

Impact:
Important
Public Date:
2021-01-26
CWE:
CWE-122: Heap-based Buffer Overflow
Bugzilla:
1917684: CVE-2021-3156 sudo: Heap buffer overflow in argument parsing
A flaw was found in sudo. A heap-based buffer overflow was found in the way sudo parses command line arguments. This flaw is exploitable by any local user who can execute the sudo command (by default, any local user can execute sudo) without authentication. Successful exploitation of this flaw could lead to privilege escalation. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Find out more about CVE-2021-3156 from the MITRE CVE dictionary dictionary and NIST NVD.

Statement

This flaw does not affect the versions of sudo shipped with Red Hat Enterprise Linux 5, because the vulnerable code was not present in these versions.

CVSS v3 metrics

CVSS3 Base Score 7.8
CVSS3 Base Metrics CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality High
Integrity Impact High
Availability Impact High

Mitigation

Red Hat Product Security strongly recommends customers to update to fixed sudo packages once they are available. For customers who cannot update immediately, the following interim partial mitigation using systemtap is suggested:

1. Install required systemtap packages and dependencies:

systemtap yum-utils kernel-devel-"$(uname -r)"

Then for RHEL 7 install kernel debuginfo, using:

debuginfo-install -y kernel-"$(uname -r)" 
Then for RHEL 8 & 6 install sudo debuginfo, using:
debuginfo-install sudo

2. Create the following systemtap script: (call the file as sudoedit-block.stap)

probe process("/usr/bin/sudo").function("main")  {
command = cmdline_args(0,0,"");
if (isinstr(command, "edit")) {
raise(9);
}
}
3. Install the script using the following command: (using root)
# nohup stap -g sudoedit-block.stap &
(This should output the PID number of the systemtap script)

This script will cause the vulnerable sudoedit binary to stop working. The sudo command will still work as usual.
The above change does not persist across reboots and must be applied after each reboot.

Please consult How to make a systemtap kernel module load persistently across reboots? (https://access.redhat.com/solutions/5752521) to learn how to
turn this into a service managed by initd.

4. Once the new fixed packages are installed, the systemtap script can be removed by killing the systemtap process. For example, by using:

# kill -s SIGTERM 7590
(where 7590 is the PID of the systemtap process)

External References

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