6.5

CVE-2026-57963: mozilla thunderbird Cross-site Scripting

CVSS: 6.5v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-57963DEBIAN-CVE-2026-57963
Published 01-07-2026Last modified 01-07-2026
Open JSON

Vulnerability summary

CVE-2026-57963 is a medium (CVSS 6.5) Cross-site Scripting vulnerability in mozilla thunderbird. EPSS estimates a 0.31% chance of exploitation in the next 30 days, higher than 21.9% 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
0.31%
0%100%
Low · +0.11 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 3 · Related 1
MGASA-2026-0243MGASA-2026-0326OPENSUSE-SU-2026:11164-1

Timeline

  1. 01-07-2026
    PublishedVulnerability first disclosed.
  2. 01-07-2026
    Last modifiedVulnerability information updated.

Description

An attacker who can send HTML chat messages (via Matrix or XMPP) can inject arbitrary styled content, phishing links, and CSS that manipulates the chat UI. This vulnerability was fixed in Thunderbird 152.0.1 and Thunderbird 140.12.1.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.31%

Chance of exploitation in the next 30 days

Percentile

22%

Versus all other CVEs

30-day change

+0.11 pp

From 0.19% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.31%

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

Debian1 product
  • thunderbird< 1:140.13.0esr-2~deb12u1 | < 1:140.13.0esr-2~deb13u1 | < 1:140.13.0esr-1
Mozilla1 product
Ubuntu1 product
  • thunderbirdAll versions (No fix recorded)

3 vendors · 3 products

References

7 links