CVE-2021-26910: Firejail before 0.9.64.4 allows attackers to bypass intended access restrictions because there is a TOCTOU rac

Q: How do I fix CVE-2021-26910?

firejail: upgrade to 0.9.64.4; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-26910 being exploited?

CVE-2021-26910 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-26910 affect?

CVE-2021-26910 affects firejail, debian linux. Severity is high (CVSS 7.8). Firejail before 0.9.64.4 allows attackers to bypass intended access restrictions because there is a TOCTOU race condition between a stat operation and an OverlayFS mount operation.

Q: How urgent is CVE-2021-26910?

Priority 47/100. High severity; Public exploit reference; On your watchlist

This month

HIGH 7.8WATCHLISTUPGRADEMITIGATE

CVE-2021-26910 is a high-severity flaw (CVSS 7.8) affecting firejail, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Firejail before 0.9.64.4 allows attackers to bypass intended access restrictions because there is a TOCTOU race condition between a stat operation and an OverlayFS mount operation.

Why this priority

High severity
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	0.4% (top 61%)
CISA exploited list	No
Weakness	CWE-367
Published	2021-02-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · firejail project

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

Am I affected?

Timeline

2021-02-08 20:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

firejail project firejail UPGRADE

Affected: < 0.9.64.4

Fixed in: 0.9.64.4

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 0.9.64.4 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firejail

Note

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

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.

Verify at the official source NVD · CVE Program · 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-2021-26910?

firejail: upgrade to 0.9.64.4; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-26910 being exploited?

CVE-2021-26910 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-26910 affect?

CVE-2021-26910 affects firejail, debian linux. Severity is high (CVSS 7.8). Firejail before 0.9.64.4 allows attackers to bypass intended access restrictions because there is a TOCTOU race condition between a stat operation and an OverlayFS mount operation.

How urgent is CVE-2021-26910?

Priority 47/100. High severity; Public exploit reference; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2022-31214 HIGH 7.8 DOWNGRADE MITIGATE A Privilege Context Switching issue was discovered in join.c in Firejail 0.9.68
CVE-2020-17368 CRITICAL 9.8 UPGRADE MITIGATE Firejail through 0.9.62 mishandles shell metacharacters during use of the --output or --output-stderr option,
CVE-2020-17367 HIGH 7.8 UPGRADE MITIGATE Firejail through 0.9.62 does not honor the -- end-of-options indicator after the --output option, which may le

References

← Back to latest CVEs