CVE-2026-84120: mozilla firefox Use After Free
CVSS: 5.4v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-84120DEBIAN-CVE-2026-84120CGA-4xpx-hrm8-q6wrCGA-7f5x-pmqp-2qcrCGA-f3c4-w585-ww3qCGA-v64f-xxjf-xcv8
Published 01-09-2026Last modified 01-09-2026
Vulnerability summary
CVE-2026-84120 is a medium (CVSS 5.4) Use After Free vulnerability in mozilla firefox. EPSS estimates a 0.22% chance of exploitation in the next 30 days, higher than 11.5% of scored vulnerabilities.
CVSS score
5.4/10
010
Medium · v3.1 (CVE.org)EPSS score
0.22%
0%100%
Low · 0.00 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 31 · Related 9MGASA-2026-0387MGASA-2026-0388OPENSUSE-SU-2026:11666-1OPENSUSE-SU-2026:11677-1OPENSUSE-SU-2026:11678-1OPENSUSE-SU-2026:21853-1RHSA-2026:67129RHSA-2026:67133RHSA-2026:68549RHSA-2026:70642RHSA-2026:73130RHSA-2026:73971RHSA-2026:76740RHSA-2026:76741RHSA-2026:76742RHSA-2026:76745RHSA-2026:76746RHSA-2026:76894RHSA-2026:76895RHSA-2026:77610RHSA-2026:77627RHSA-2026:77631RHSA-2026:77632RHSA-2026:80503RHSA-2026:81912RHSA-2026:81913RHSA-2026:82122SUSE-SU-2026:23784-1SUSE-SU-2026:4140-1SUSE-SU-2026:4156-1SUSE-SU-2026:4268-1CGA-34JG-6G2F-W52M
Timeline
- 01-09-2026PublishedVulnerability first disclosed.
- 01-09-2026Last modifiedVulnerability information updated.
Description
Use-after-free in the Audio/Video component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
CVSS metrics
4 scores · 4 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 4 agree
- OSV · UbuntuEcosystem advisory · calculated5.4MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- OSV · DebianEcosystem 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
0.22%
Chance of exploitation in the next 30 days
Percentile
12%
Versus all other CVEs
30-day change
0.00 pp
From 0.22% on 19-09-2026
19-09-202619-10-2026
EPSS score0.22%
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
Debian2 products
- firefox-esr< 140.15.0esr-1~deb12u1 | < 140.15.0esr-1~deb13u1 | < 140.15.0esr-1
- thunderbird< 1:140.15.0esr-1~deb12u1 | < 1:140.15.0esr-1~deb13u1 | < 1:153.2.0esr-1
Mozilla2 products
- firefox< 115.40.0 | ≥ 116.0, < 140.15.0 | ≥ 141.0.0, < 153.2.0 | ≥ 154.0.0, < 155.0.0
- thunderbird< 140.15.0 | ≥ 141.0, < 153.2.0 | ≥ 154.0, < 155.0
Wolfi2 products
- firefox< 155.0.1-r0
- firefox-docker-selenium-compat< 155.0.1-r0
5 vendors · 16 products
References
12 links- bugzilla.mozilla.org/show_bug.cgi?id=2058911Permissions Required
- www.mozilla.org/security/advisories/mfsa2026-82/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-83/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-84/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/mfsa2026-87/Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-88/Vendor Advisory
