What is CVE-2026-12321?
JIT miscompilation in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 152 and Thunderbird 152.
The record classifies CVE-2026-12321 under weakness class CWE-670. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 116 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 5.4 — MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N - EPSS (FIRST)
- 0.1% probability of exploitation in the next 30 days, higher than 4.4% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 2.9/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-06-16
Is CVE-2026-12321 being exploited?
It currently carries a trending score of 7 in the Threadlinqs vulnerability feed.
Affected products and versions
- Mozilla: Firefox, Thunderbird
How to fix CVE-2026-12321
No vendor patch reference has been recorded for CVE-2026-12321 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-12321
1 tracked threat in the Threadlinqs corpus references CVE-2026-12321, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on .