9.8

CVE-2026-84140: mozilla firefox Origin Validation Error

CVSS: 9.8v3.1CriticalModified
AliasesUBUNTU-CVE-2026-84140CGA-3vpf-976f-hxp6CGA-ppwh-5j6r-v657
Published 01-09-2026Last modified 03-09-2026
Open JSON

Vulnerability summary

CVE-2026-84140 is a critical (CVSS 9.8) Origin Validation Error vulnerability in mozilla firefox. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 7.3% of scored vulnerabilities.

Overall risk
70/100
0100
High · default modelHow is this calculated?
CVSS score
9.8/10
010
Critical · v3.1 (CVE.org)
EPSS score
0.18%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 10 · Related 9
MGASA-2026-0387MGASA-2026-0388OPENSUSE-SU-2026:11666-1OPENSUSE-SU-2026:11677-1OPENSUSE-SU-2026:12098-1OPENSUSE-SU-2026:21853-1

Timeline

  1. 01-09-2026
    PublishedVulnerability first disclosed.
  2. 03-09-2026
    Last modifiedVulnerability information updated.

Description

Site isolation 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 version

EPSS trend

Probability

0.18%

Chance of exploitation in the next 30 days

Percentile

7%

Versus all other CVEs

30-day change

0.00 pp

From 0.18% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.18%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

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
Wolfi2 products
  • firefox< 155.0.1-r0
  • firefox-docker-selenium-compat< 155.0.1-r0

4 vendors · 14 products

References

8 links