Improper handling of CSS at-rules in lettersanitizer

Exploitation

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

CVSS

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

EPSS

• CVE-2022-31103: 1.53% estimated exploitation activity in the next 30 days; percentile 74.71 (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.

Impact All versions of lettersanitizer below 1.0.2 are affected by a denial of service issue when processing a CSS at-rule @keyframes. This package is depended on by react-letter, therefore everyone using react-letter is also at risk. Patches The problem has been patched in version 1.0.2. Workarounds There is no workaround besides upgrading. References The issue was originally reported in the react-letter repository: https://github.com/mat-sz/react-letter/issues/17 For more information If you have any questions or comments about this advisory: Open an issue in lettersanitizer Email me at contact@matsz.dev

Published by the source

23 Jun 2022, 17:48 UTC

Last modified by the source

8 Nov 2023, 04:09 UTC

Source last checked

26 Oct 2026, 12:16 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-7r3r-gq8p-v9jj

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-7r3r-gq8p-v9jj

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2022-31103

Advisory: Improper handling of CSS at-rules in lettersanitizer
IDs: CVE-2022-31103, GHSA-7r3r-gq8p-v9jj
Record: https://patchnext.com/advisories/cve-2022-31103 (revision 2, source checked 26 Oct 2026, 12:16 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lettersanitizer 1.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm lettersanitizer: affected < 1.0.2; fixed in 1.0.2

## Suggested inspection (read-only)
- `npm ls lettersanitizer --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## 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 lettersanitizer.
- 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://osv.dev/vulnerability/GHSA-7r3r-gq8p-v9jj (OSV record GHSA-7r3r-gq8p-v9jj lists affected ranges: npm lettersanitizer >=0 <1.0.2 (fixed))
- Verified: https://github.com/advisories/GHSA-7r3r-gq8p-v9jj (GitHub-reviewed advisory GHSA-7r3r-gq8p-v9jj lists affected ranges: npm lettersanitizer >=0 <1.0.2)

Commands are suggestions: review each one before running it.