^{CVE-2021-3156:}Heap-based buffer overflow vulnerability in Sudo allows privilege escalation to root via "sudoedit -s" command.

Overview

The vulnerability (CVE-2021-3156) exists in the Sudo command, a core utility in Unix/Linux systems that allows users to run programs with the security privileges of another user. The flaw is caused by an off-by-one error in the handling of escape characters in command arguments. When a user executes "sudoedit -s" with a command-line argument ending in a single backslash, it triggers a heap-based buffer overflow condition.

This vulnerability is particularly dangerous because:

1. Sudo is installed by default on almost all Unix and Linux distributions
2. The attack can be executed by any local user, even without prior sudo permissions
3. Successful exploitation results in complete root access to the system
4. The vulnerability has existed in Sudo code since July 2011

The flaw was discovered by researchers at Qualys security team and publicly disclosed in January 2021.

Remediation

To mitigate this vulnerability, system administrators should take the following actions:

1. Update Sudo to version 1.9.5p2 or later immediately through your system's package manager:

   • For Debian/Ubuntu: apt update && apt upgrade sudo
   • For RHEL/CentOS: yum update sudo
   • For Fedora: dnf update sudo
   • For macOS: Apply the security update provided by Apple

2. If immediate patching is not possible:

   • Restrict sudo access to only trusted users
   • Monitor system logs for unusual sudo usage patterns
   • Consider implementing additional access controls and monitoring

3. Verify the update was successful by checking the sudo version:

   • Run sudo -V and confirm the version is 1.9.5p2 or later

4. For systems that cannot be updated, consider implementing network segmentation to isolate vulnerable systems and enhance monitoring for potential exploitation attempts.

References

1. Sudo security advisory: https://www.sudo.ws/stable.html#1.9.5p2
2. Qualys security advisory: https://www.openwall.com/lists/oss-security/2021/01/26/3
3. CERT Vulnerability Note: https://www.kb.cert.org/vuls/id/794544
4. Debian Security Advisory: https://www.debian.org/security/2021/dsa-4839
5. Technical analysis and exploit details: http://packetstormsecurity.com/files/161160/Sudo-Heap-Based-Buffer-Overflow.html
6. Apple security update information: https://support.apple.com/kb/HT212177
7. Cisco advisory for affected products: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sudo-privesc-jan2021-qnYQfcM