CVE-2021-45707: An issue was discovered in the nix crate 0.16.0 and later before 0.20.2, 0.21.x before 0.21.2, and 0.22.x befo

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CRITICAL 9.8REMOTEUPGRADE

CVE-2021-45707 is a critical-severity flaw (CVSS 9.8) affecting nix. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the nix crate 0.16.0 and later before 0.20.2, 0.21.x before 0.21.2, and 0.22.x before 0.22.2 for Rust. unistd::getgrouplist has an out-of-bounds write if a user is in more than 16 /etc/groups groups.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Weakness	CWE-787
Published	2021-12-27
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: nix project

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

Am I affected?

Timeline

2021-12-27 00:15 UTCPublished CVE record published
2026-06-17 04:13 UTCUpdated Record last modified

nix project nix UPGRADE

Affected: >= 0.16.0 and < 0.20.2 · >= 0.21.0 and < 0.21.2 · >= 0.22.0 and < 0.22.2

Fixed in: 0.20.2, 0.21.2, 0.22.2

Safe to downgrade to: a release before 0.16.0

1. Check installed version

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

2. UPGRADE to 0.20.2 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nix

Note

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

3. If no update is available yet, DOWNGRADE to a release before 0.16.0 (Debian / Ubuntu)

apt-cache madison nix sudo apt install nix=<VERSION_BEFORE_0.16.0> sudo apt-mark hold nix

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nix sudo dnf downgrade nix-<VERSION_BEFORE_0.16.0> sudo dnf versionlock add nix

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2021-45707?

nix: upgrade to 0.20.2, 0.21.2, 0.22.2. Exact commands for each OS are on this page.

Is CVE-2021-45707 being exploited?

CVE-2021-45707 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-2021-45707 affect?

CVE-2021-45707 affects nix. Severity is critical (CVSS 9.8). An issue was discovered in the nix crate 0.16.0 and later before 0.20.2, 0.21.x before 0.21.2, and 0.22.x before 0.22.2 for Rust. unistd::getgrouplist has an out-of-bounds write if a user is in more than 16 /etc/groups groups.

How urgent is CVE-2021-45707?

Priority 59/100. Critical severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-39860 CRITICAL 9.0 UPGRADE Nix is a package manager for Linux and other Unix systems
CVE-2024-45593 CRITICAL 9.0 UPGRADE Nix is a package manager for Linux and other Unix systems
CVE-2024-27297 MEDIUM 6.3 UPGRADE Nix is a package manager for Linux and other Unix systems

References

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