What’s Vulnerable › Vulnerabilities

CVE-2021-29964

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-24 · updated 2026-06-17
• Weakness: CWE-125

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.

Affected products

• Mozilla Firefox: before 89.0 — fixed in 89.0
• Mozilla Firefox ESR: before 78.11 — fixed in 78.11
• Mozilla Thunderbird: before 78.11 — fixed in 78.11

How to fix

Upgrade to a fixed version: Mozilla Firefox 89.0; Mozilla Firefox ESR 78.11; Mozilla Thunderbird 78.11. Check the vendor advisory for mitigations.

References

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

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