What’s Vulnerable › Vulnerabilities

CVE-2021-29984

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-08-17 · updated 2026-06-17
• Weakness: CWE-787

Description

Instruction reordering resulted in a sequence of instructions that would cause an object to be incorrectly considered during garbage collection. This led to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13, and Firefox < 91.

Affected products

• Mozilla Firefox: before 91.0 — fixed in 91.0
• Mozilla Firefox ESR: before 78.13.0 — fixed in 78.13.0
• Mozilla Thunderbird: before 78.13.0 — fixed in 78.13.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 91.0; Mozilla Firefox ESR 78.13.0; Mozilla Thunderbird 78.13.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1720031
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-33/
• https://www.mozilla.org/security/advisories/mfsa2021-34/
• https://www.mozilla.org/security/advisories/mfsa2021-35/
• https://www.mozilla.org/security/advisories/mfsa2021-36/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1720031
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-33/
• https://www.mozilla.org/security/advisories/mfsa2021-34/

Get alerted when CVE-2021-29984 or the next vulnerability affects your stack