CVE-2026-84118: mozilla firefox Use After Free
CVSS: 5.4v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-84118CGA-286p-8p4p-2464CGA-9x8q-mm7m-pjvfCGA-j6jx-hvj3-3q6wCGA-qq8r-cq2p-qh4r
Published 01-09-2026Last modified 01-09-2026
Vulnerability summary
CVE-2026-84118 is a medium (CVSS 5.4) Use After Free vulnerability in mozilla firefox. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 19.9% of scored vulnerabilities.
CVSS score
5.4/10
010
Medium · v3.1 (CVE.org)EPSS score
0.29%
0%100%
Low · +0.08 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 10 · Related 9Timeline
- 01-09-2026PublishedVulnerability first disclosed.
- 01-09-2026Last modifiedVulnerability information updated.
Description
Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
CVSS metrics
3 scores · 3 sources · 1 versionMedium 5.4Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:NSourcesAll 3 agree
- OSV · UbuntuEcosystem advisory · calculated5.4MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- NVDNIST5.4MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
EPSS trend
Probability
0.29%
Chance of exploitation in the next 30 days
Percentile
20%
Versus all other CVEs
30-day change
+0.08 pp
From 0.20% on 19-09-2026
19-09-202619-10-2026
EPSS score0.29%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Ubuntu8 products
- mozjs102All versions (No fix recorded)
- mozjs115All versions (No fix recorded)
- mozjs38All versions (No fix recorded)
- mozjs52All versions (No fix recorded)
- mozjs68All versions (No fix recorded)
Chainguard2 products
- firefox< 155.0.1-r0
- firefox-docker-selenium-compat< 155.0.1-r0
Mozilla2 products
- firefox< 153.2.0 | ≥ 154.0.0, < 155.0.0
- thunderbird< 153.2.0 | ≥ 154.0, < 155.0
Wolfi2 products
- firefox< 155.0.1-r0
- firefox-docker-selenium-compat< 155.0.1-r0
4 vendors · 14 products
References
8 links- bugzilla.mozilla.org/show_bug.cgi?id=2057457Permissions Required
- www.mozilla.org/security/advisories/mfsa2026-82/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-85/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-86/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-88/Vendor Advisory