CVE-2021-3156: Sudo Heap-Based Buffer Overflow Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 6 Apr 2022, 435 days after the CVE record was published.

How likely is exploitation in the next 30 days?

100%

EPSS score, percentile 100 of all scored records

How severe?

7.8 High

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA deadline 27 Apr 2022. Apply updates per vendor instructions.

Advisories and patches (5)

Which versions are affected?

Not stated. The CVE record gives vendor and product as “n/a” and the version as “unspecified”.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 27 April 2022.

Advisories and patches

• GLSA-202101-33 (Vendor advisory)
• DSA-4839 (Vendor advisory)
• FEDORA-2021-2cb63d912a (Vendor advisory)
• FEDORA-2021-8840cbdccd (Vendor advisory)
• 20210129 Sudo Privilege Escalation Vulnerability Affecting Cisco Products: January 2021 (Vendor advisory)

Linked from CISA's catalog entry

• https://nvd.nist.gov/vuln/detail/CVE-2021-3156

Affected products and versions

The CVE record does not name affected products or versions: vendor and product are “n/a” and the version is “unspecified”.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

Sudo contains an off-by-one error that can result in a heap-based buffer overflow, which allows for privilege escalation.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2021-3156 to its Known Exploited Vulnerabilities (KEV) catalog on 6 Apr 2022.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 27 Apr 2022.
• The CVE record was published on 26 Jan 2021, 435 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 7.8 (High), taken from CISA's enrichment of the record.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 100% (percentile 100), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

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.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-193: Off-by-one Error
• CWE-122

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

References

• VU#794544 (Third-party advisory)
• [debian-lts-announce] 20210126 [SECURITY] [DLA 2534-1] sudo security update
• 20210126 Baron Samedit: Heap-based buffer overflow in Sudo (CVE-2021-3156)
• [oss-security] 20210126 Baron Samedit: Heap-based buffer overflow in Sudo (CVE-2021-3156)
• [oss-security] 20210127 Re: Baron Samedit: Heap-based buffer overflow in Sudo (CVE-2021-3156)
• [oss-security] 20210127 Re: Baron Samedit: Heap-based buffer overflow in Sudo (CVE-2021-3156)
• 20210211 APPLE-SA-2021-02-09-1 macOS Big Sur 11.2.1, macOS Catalina 10.15.7 Supplemental Update, and macOS Mojave 10.14.6 Security Update 2021-002

22 more in the CVE record.

More exploited Sudo vulnerabilities

• CVE-2025-32463: Sudo Inclusion of Functionality from Untrusted Control Sphere Vulnerability (added 29 Sep 2025)