CVE-2021-3156
HIGHCISA KEVEPSS 100th pctlDescription
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.
How to fix
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 100% of all known CVEs.
Sudo Heap-Based Buffer Overflow Vulnerability
Sudo contains an off-by-one error that can result in a heap-based buffer overflow, which allows for privilege escalation.
Apply updates per vendor instructions.
Remediation due: 2022-04-27
References
Related Vulnerabilities
Other CWE-193 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2003-0466 | Critical | 9.8 | 78% | - | - |
| CVE-2023-44444 | High | 7.8 | 56% | - | Fix |
| CVE-2021-23017 | High | 7.7 | 53% | - | Fix |
| CVE-2023-28709 | High | 7.5 | 48% | - | Fix |
| CVE-2018-8828 | Critical | 9.8 | 30% | - | Fix |
| CVE-2001-0609 | Critical | 9.8 | 18% | - | - |
Common questions
How do I fix CVE-2021-3156?
Published advisories record a fix for 6 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-3156 being actively exploited?
Yes. CVE-2021-3156 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. US federal agencies were required to remediate it by 2022-04-27. Treat it as a priority whatever its CVSS score says.
How severe is CVE-2021-3156?
CVE-2021-3156 has a CVSS v3 base score of 7.8, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-3156 affect?
Published advisories record a fix for sudo (Amazon), sudo-debuginfo (Amazon), sudo-devel (Amazon), sudo (Debian), and 2 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2021-3156
Markdown
[](https://tridentstack.com/cve/CVE-2021-3156)HTML
<a href="https://tridentstack.com/cve/CVE-2021-3156"><img src="https://tridentstack.com/cve/badge/CVE-2021-3156.svg" alt="CVE-2021-3156"></a>This vulnerability is actively exploited in the wild
TridentStack Control detects known-exploited CVEs across your Linux fleet and prioritizes their patches. 200 endpoints free forever.
This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.