CVE-2021-29981

Name: CVE-2021-29981
Creator: NVD / NIST
Published: 2021-08-17T20:15:07.73+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 1.00%

Last modified Jun 17, 2026

CVE-2021-29981 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. 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.. EPSS estimates a 1.00% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

8.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS Probability

1.00%

58.5th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 91.0
Mozilla	Thunderbird	< 91.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1707774Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-36/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1707774Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-36/Vendor Advisory

Timeline

Published: Aug 17, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29981?

How severe is CVE-2021-29981?

CVE-2021-29981 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 1.00% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29981?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29981?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST