comm: lossy UTF-8 conversion silently corrupts non-UTF-8 output

Exploitation

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

CVSS

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

EPSS

• CVE-2026-35346: 0.18% estimated exploitation activity in the next 30 days; percentile 7.15 (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.

The comm utility in uutils coreutils silently corrupts data by performing lossy UTF-8 conversion on all output lines. The implementation uses String::fromutf8lossy(), which replaces invalid UTF-8 byte sequences with the Unicode replacement character (U+FFFD). This behavior differs from GNU comm, which processes raw bytes and preserves the original input. This results in corrupted output when the utility is used to compare binary files or files using non-UTF-8 legacy encodings. --- Zellic finding 3.34. Reported in the Zellic uutils coreutils Program Security Assessment (for Canonical, Jan 2026), audited commit 3a07ffc5a9bd4c283e75afa548ba1f1957bad242.

Published by the source

6 Jul 2026, 19:51 UTC

Last modified by the source

6 Jul 2026, 19:51 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6gcw-w7cp-94g9

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# Patch Next advisory brief: CVE-2026-35346

Advisory: comm: lossy UTF-8 conversion silently corrupts non-UTF-8 output
IDs: CVE-2026-35346, GHSA-6gcw-w7cp-94g9
Record: https://patchnext.com/advisories/cve-2026-35346 (revision 1, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: uu_comm 0.6.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io uu_comm: affected < 0.6.0; fixed in 0.6.0

## Suggested inspection (read-only)
- crates.io uu_comm: 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 uu_comm.
- 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-6gcw-w7cp-94g9 (GitHub-reviewed advisory GHSA-6gcw-w7cp-94g9 lists affected ranges: crates.io uu_comm >=0 <0.6.0)

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