What’s Vulnerable › Vulnerabilities

CVE-2021-29976

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-05 · updated 2026-06-17
• Weakness: CWE-787

Description

Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. 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 Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.

Affected products

• Mozilla Firefox: before 90.0 — fixed in 90.0
• Mozilla Firefox ESR: before 78.12 — fixed in 78.12
• Mozilla Thunderbird: before 78.12 — fixed in 78.12

How to fix

Upgrade to a fixed version: Mozilla Firefox 90.0; Mozilla Firefox ESR 78.12; Mozilla Thunderbird 78.12. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1700895%2C1703334%2C1706910%2C1711576%2C1714391
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-28/
• https://www.mozilla.org/security/advisories/mfsa2021-29/
• https://www.mozilla.org/security/advisories/mfsa2021-30/
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1700895%2C1703334%2C1706910%2C1711576%2C1714391
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.mozilla.org/security/advisories/mfsa2021-28/
• https://www.mozilla.org/security/advisories/mfsa2021-29/
• https://www.mozilla.org/security/advisories/mfsa2021-30/

Get alerted when CVE-2021-29976 or the next vulnerability affects your stack