RUSTSEC-2021-0119: Out-of-bounds write in nix::unistd::getgrouplist

What to do

1. See which version you have: cargo tree -i nix (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p nix. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example nix = "0.23.0") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

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, which is usually only editable by the root user.

References

• Package: crates.io/crates/nix
• Advisory: rustsec.org/advisories/RUSTSEC-2021-0119.html
• Report: github.com/nix-rust/nix/issues/1541

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.