6.5

CVE-2025-6429: mozilla firefox Improper Encoding or Escaping of Output

CVSS: 6.5v3.1MediumModified
AliasesUBUNTU-CVE-2025-6429DEBIAN-CVE-2025-6429CGA-pchg-4rgv-w38j
Published 24-06-2025Last modified 13-04-2026
Open JSON

Vulnerability summary

CVE-2025-6429 is a medium (CVSS 6.5) Improper Encoding or Escaping of Output vulnerability in mozilla firefox. EPSS estimates a 0.36% chance of exploitation in the next 30 days, higher than 27.7% of scored vulnerabilities.

Overall risk
26/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.5/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.36%
0%100%
Low · +0.03 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 41 · Related 15
DLA-4231-1DLA-4239-1DSA-5950-1DSA-5959-1MGASA-2025-0201MGASA-2025-0228

Timeline

  1. 24-06-2025
    PublishedVulnerability first disclosed.
  2. 13-04-2026
    Last modifiedVulnerability information updated.

Description

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an `embed` tag. This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

CVSS metrics

6 scores · 6 sources · 1 version

EPSS trend

Probability

0.36%

Chance of exploitation in the next 30 days

Percentile

28%

Versus all other CVEs

30-day change

+0.03 pp

From 0.33% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.36%

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< 128.12-r0
  • firefox-esr< 128.12-r0
Debian2 products
  • firefox-esr< 128.12.0esr-1~deb12u1 | < 128.12.0esr-1
  • thunderbird< 1:128.12.0esr-1~deb12u1 | < 1:128.12.0esr-1
Mozilla1 product
Wolfi1 product
  • firefox< 128.12-r0

5 vendors · 14 products

References

13 links
Show all 13 references