CVE-2021-29981

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-08-17 · updated 2026-06-17

Description

An issue present in lowering/register allocation could have led to obscure but deterministic register confusion failures in JITted code that would lead to a potentially exploitable crash. This vulnerability affects Firefox < 91 and Thunderbird < 91.

Affected products

Mozilla Firefox: before 91.0 — fixed in 91.0
Mozilla Thunderbird: before 91.0 — fixed in 91.0

How to fix

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

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1707774
https://security.gentoo.org/glsa/202202-03
https://www.mozilla.org/security/advisories/mfsa2021-33/
https://www.mozilla.org/security/advisories/mfsa2021-36/
https://bugzilla.mozilla.org/show_bug.cgi?id=1707774
https://security.gentoo.org/glsa/202202-03
https://www.mozilla.org/security/advisories/mfsa2021-33/
https://www.mozilla.org/security/advisories/mfsa2021-36/

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