Out-of-bounds Write in nix

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.7 · CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2021-45707: 1.69% estimated exploitation activity in the next 30 days; percentile 77.10 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

On certain platforms, if a user has more than 16 groups, the nix::unistd::getgrouplist function will call the libc getgrouplist function with a length parameter greater than the size of the buffer it provides, resulting in an out-of-bounds write and memory corruption. The libc getgrouplist function takes an in/out parameter ngroups specifying the size of the group buffer. When the buffer is too small to hold all of the requested user's group memberships, some libc implementations, including glibc and Solaris libc, will modify ngroups to indicate the actual number of groups for the user, in addition to returning an error. The version of nix::unistd::getgrouplist in nix 0.16.0 and up will resize the buffer to twice its size, but will not read or modify the ngroups variable. Thus, if the user has more than twice as many groups as the initial buffer size of 8, the next call to getgrouplist will then write past the end of the buffer. The issue would require editing /etc/groups to exploit,…

Published by the source

6 Jan 2022, 22:07 UTC

Last modified by the source

21 Feb 2024, 19:15 UTC

Source last checked

26 Oct 2026, 15:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-76w9-p8mg-j927

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# Patch Next advisory brief: CVE-2021-45707

Advisory: Out-of-bounds Write in nix
IDs: CVE-2021-45707, GHSA-76w9-p8mg-j927
Record: https://patchnext.com/advisories/cve-2021-45707 (revision 1, source checked 26 Oct 2026, 15:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nix 0.22.2, 0.21.2, 0.20.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io nix: affected >= 0.21.0, < 0.21.2; >= 0.22.0, < 0.22.2; >= 0.16.0, < 0.20.2; fixed in 0.20.2, 0.22.2, 0.21.2

## Suggested inspection (read-only)
- crates.io nix: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nix.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-76w9-p8mg-j927 (GitHub-reviewed advisory GHSA-76w9-p8mg-j927 lists affected ranges: crates.io nix >=0.21.0 =0.22.0 =0.16.0 <0.20.2)

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