CVE-2026-84136: mozilla firefox Cross-site Scripting
CVSS: 9.8v3.1CriticalModified
AliasesUBUNTU-CVE-2026-84136CGA-fh3q-4fvh-w233CGA-r7pg-xq99-2w25CGA-v5vx-8wxh-fqvrCGA-vpmx-f577-fq32
Published 01-09-2026Last modified 03-09-2026
Vulnerability summary
CVE-2026-84136 is a critical (CVSS 9.8) Cross-site Scripting vulnerability in mozilla firefox. EPSS estimates a 0.20% chance of exploitation in the next 30 days, higher than 9.6% of scored vulnerabilities.
CVSS score
9.8/10
010
Critical · v3.1 (CVE.org)EPSS score
0.20%
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 10 · Related 9Timeline
- 01-09-2026PublishedVulnerability first disclosed.
- 03-09-2026Last modifiedVulnerability information updated.
Description
Other issue in the DOM: Navigation 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 versionCritical 9.8Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSources3 sources · 6.1–9.8
- OSV · UbuntuEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- NVDNIST6.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NDiffers
EPSS trend
Probability
0.20%
Chance of exploitation in the next 30 days
Percentile
10%
Versus all other CVEs
30-day change
0.00 pp
From 0.20% on 19-09-2026
19-09-202619-10-2026
EPSS score0.20%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
- CWE-200Exposure of Sensitive Information to an Unauthorized ActorThe product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
Affected 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- 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