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

Q: How do I fix CVE-2021-3156?

sudo: upgrade to 1.8.32, 1.9.5; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-3156 being exploited?

Yes. CVE-2021-3156 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2021-3156 affect?

CVE-2021-3156 affects sudo, fedora, debian linux. Severity is high (CVSS 7.8). 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.

Q: How urgent is CVE-2021-3156?

Priority 87/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Patch now

HIGH 7.8EXPLOITEDWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-3156 is a high-severity flaw (CVSS 7.8) affecting sudo, fedora, debian linux, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	100.0% (top 1%)
CISA exploited list	Yes, fix due 2022-04-27
Weakness	CWE-193
Published	2021-01-26
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · fedoraproject · netapp · sudo project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-01-26 21:15 UTCPublished CVE record published
2022-04-06Exploited Added to the CISA Known Exploited Vulnerabilities list
2022-04-27Deadline CISA due date for US federal agencies to patch
2026-06-17 04:04 UTCUpdated Record last modified

sudo project sudo UPGRADE

Affected: >= 1.8.2 and < 1.8.32 · >= 1.9.0 and < 1.9.5 · 1.9.5 · 1.9.5 patch1

Fixed in: 1.8.32, 1.9.5

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy sudo || rpm -q sudo || sudo --version

2. UPGRADE to 1.8.32 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade sudo

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade sudo

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 32 · 33

Fixed in: no fixed release known

Safe to downgrade to: a release before 32

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp active iq unified manager MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy active-iq-unified-manager || rpm -q active-iq-unified-manager || active-iq-unified-manager --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

netapp cloud backup MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy cloud-backup || rpm -q cloud-backup || cloud-backup --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

netapp hci management node MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy hci-management-node || rpm -q hci-management-node || hci-management-node --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · feh · FIXED · 3.13.1-1.fc46 · FEDORA-2026-3c76a13a4f · source

sudo dnf upgrade --advisory=FEDORA-2026-3c76a13a4f

Fedora ELN · setroubleshoot · FIXED · 3.3.37-7.eln159 · FEDORA-2026-f81b122fe1 · source

sudo dnf upgrade --advisory=FEDORA-2026-f81b122fe1

Ubuntu 20.04 · sudo · FIXED · 1.8.31-1ubuntu1.2

sudo apt update && sudo apt install --only-upgrade sudo dpkg --compare-versions "$(dpkg-query -W -f='${Version}' sudo)" ge "1.8.31-1ubuntu1.2" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · sudo · FIXED · 1.9.5p1-1.1

sudo apt update && sudo apt install --only-upgrade sudo dpkg --compare-versions "$(dpkg-query -W -f='${Version}' sudo)" ge "1.9.5p1-1.1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · sudo · FIXED · 1.9.5p1-1.1

sudo apt update && sudo apt install --only-upgrade sudo dpkg --compare-versions "$(dpkg-query -W -f='${Version}' sudo)" ge "1.9.5p1-1.1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 6 Extended Lifecycle Support · sudo · FIXED · sudo-1.8.6p3-29.el6_10.4

sudo dnf upgrade --advisory=RHSA-2021:0227 rpm -q sudo

RHEL 7 · sudo · FIXED · sudo-1.8.23-10.el7_9.1

sudo dnf upgrade --advisory=RHSA-2021:0221 rpm -q sudo

RHEL 7.2 Advanced Update Support · sudo · FIXED · sudo-1.8.6p7-17.el7_2.3

sudo dnf upgrade --advisory=RHSA-2021:0226 rpm -q sudo

RHEL 7.3 Advanced Update Support · sudo · FIXED · sudo-1.8.6p7-23.el7_3.3

sudo dnf upgrade --advisory=RHSA-2021:0225 rpm -q sudo

RHEL 7.4 Advanced Update Support · sudo · FIXED · sudo-1.8.19p2-12.el7_4.2

sudo dnf upgrade --advisory=RHSA-2021:0224 rpm -q sudo

Alpine 3.20 · sudo · FIXED · sudo-1.9.5_p2-r0

apk add --upgrade sudo apk info -v sudo

Alpine 3.21 · sudo · FIXED · sudo-1.9.5_p2-r0

apk add --upgrade sudo apk info -v sudo

Alpine 3.22 · sudo · FIXED · sudo-1.9.5_p2-r0

apk add --upgrade sudo apk info -v sudo

Alpine 3.23 · sudo · FIXED · sudo-1.9.5_p2-r0

apk add --upgrade sudo apk info -v sudo

Amazon Linux 2 · see advisory · FIXED · ALAS2-2021-1590 · source

sudo yum update --advisory=ALAS2-2021-1590

Amazon Linux 1 · see advisory · FIXED · ALAS-2021-1478 · source

sudo yum update --advisory=ALAS-2021-1478

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: blasty/CVE-2021-3156 (1031 stars)
GitHub PoC: worawit/CVE-2021-3156 (810 stars)
GitHub PoC: stong/CVE-2021-3156 (430 stars)
Write-up: kc.mcafee.com/corporate/index?page=content&id=SB10348
Write-up: www.oracle.com//security-alerts/cpujul2021.html
Exploit-DB: Sudo 1.9.5p1 - 'Baron Samedit ' Heap-Based Buffer Overflow Privilege Escalation (1)
Exploit-DB: Sudo 1.9.5p1 - 'Baron Samedit ' Heap-Based Buffer Overflow Privilege Escalation (2)
Metasploit: Sudo Heap-Based Buffer Overflow

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-3156?

sudo: upgrade to 1.8.32, 1.9.5; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-3156 being exploited?

Yes. CVE-2021-3156 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2021-3156 affect?

CVE-2021-3156 affects sudo, fedora, debian linux. Severity is high (CVSS 7.8). 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 urgent is CVE-2021-3156?

Priority 87/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Software pages

Debian vulnerabilities · Sudo vulnerabilities

Related CVEs

CVE-2026-35535 HIGH 7.4 UPGRADE UPGRADE In Sudo through 1.9.17p2 before 3e474c2, a failure of a setuid, setgid, or setgroups call, during a privilege
CVE-2025-32462 LOW 2.8 UPGRADE Sudo before 1.9.17p1, when used with a sudoers file that specifies a host that is neither the current host nor
CVE-2025-46718 LOW 3.3 UPGRADE sudo-rs is a memory safe implementation of sudo and su written in Rust
CVE-2025-46717 LOW 3.3 UPGRADE sudo-rs is a memory safe implementation of sudo and su written in Rust
CVE-2025-32463 CRITICAL 9.3 EXPLOITED UPGRADE MITIGATE Sudo Inclusion of Functionality from Untrusted Control Sphere Vulnerability

References

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