CVE-2021-29964

Name: CVE-2021-29964
Creator: NVD / NIST
Published: 2021-06-24T14:15:10.333+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.1/10EPSS 0.79%

Last modified Jun 17, 2026

CVE-2021-29964 is a high-severity vulnerability rated 7.1/10 on the CVSS scale. A locally-installed hostile program could send `WM_COPYDATA` messages that Firefox would process incorrectly, leading to an out-of-bounds read. *This bug only affects Firefox on Windows. EPSS estimates a 0.79% chance of exploitation in the next 30 days.

Description

A locally-installed hostile program could send `WM_COPYDATA` messages that Firefox would process incorrectly, leading to an out-of-bounds read. *This bug only affects Firefox on Windows. Other operating systems are unaffected.*. This vulnerability affects Thunderbird < 78.11, Firefox < 89, and Firefox ESR < 78.11.

Metrics

CVSS 3.1

7.1/10

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

EPSS Probability

0.79%

51.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-125

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 89.0
Mozilla	Firefox Esr	< 78.11
Mozilla	Thunderbird	< 78.11

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1706501Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-23/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-24/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-26/Release Notes, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1706501Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-23/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-24/Release Notes, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-26/Release Notes, Vendor Advisory

Timeline

Published: Jun 24, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29964?

How severe is CVE-2021-29964?

CVE-2021-29964 has a CVSS score of 7.1/10 (HIGH severity). The EPSS model estimates a 0.79% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29964?

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-2021-29964?

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

Scan your code now

Source: NVD / NIST