CVE-2021-29984

Name: CVE-2021-29984
Creator: NVD / NIST
Published: 2021-08-17T20:15:07.85+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 1.39%

Last modified Jun 17, 2026

CVE-2021-29984 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. 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. EPSS estimates a 1.39% chance of exploitation in the next 30 days.

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.

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

1.39%

68.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 91.0
Mozilla	Firefox Esr	< 78.13.0
Mozilla	Thunderbird	< 78.13.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1720031Exploit, Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-34/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-35/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-36/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1720031Exploit, Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-33/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-34/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-35/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-2021-29984?

How severe is CVE-2021-29984?

CVE-2021-29984 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 1.39% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29984?

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-2021-29984?

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

Scan your code now

Source: NVD / NIST