CVE-2021-29964
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.82%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.1 HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
- EPSS
- 0.82% probability · 57th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-125
- Affected
- mozilla/firefox · mozilla/firefox esr · mozilla/thunderbird
- Source
- security@mozilla.org
EPSS 0.8% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.