CVE-2021-23960
Performing garbage collection on re-declared JavaScript variables resulted in a user-after-poison, and a potentially exploitable crash.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.29%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
Performing garbage collection on re-declared JavaScript variables resulted in a user-after-poison, and a potentially exploitable crash. This vulnerability affects Firefox < 85, Thunderbird < 78.7, and Firefox ESR < 78.7.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS
- 1.29% probability · 70th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- mozilla/firefox · mozilla/firefox esr · mozilla/thunderbird
- Source
- security@mozilla.org
EPSS 1.3% 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=1675755Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-04/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-05/Release Notes, Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1675755Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-04/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-05/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.