7.5

CVE-2026-84640: mozilla thunderbird Buffer Over-read

CVSS: 7.5v3.1HighAnalyzed
AliasesUBUNTU-CVE-2026-84640DEBIAN-CVE-2026-84640
Published 01-09-2026Last modified 02-09-2026
Open JSON

Vulnerability summary

CVE-2026-84640 is a high (CVSS 7.5) Buffer Over-read vulnerability in mozilla thunderbird. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 17% of scored vulnerabilities.

Overall risk
30/100
0100
Medium · default modelHow is this calculated?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
0.26%
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 13 · Related 2
MGASA-2026-0388OPENSUSE-SU-2026:11678-1RHSA-2026:70642RHSA-2026:73130RHSA-2026:73971RHSA-2026:77627

Timeline

  1. 01-09-2026
    PublishedVulnerability first disclosed.
  2. 02-09-2026
    Last modifiedVulnerability information updated.

Description

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.26%

Chance of exploitation in the next 30 days

Percentile

17%

Versus all other CVEs

30-day change

0.00 pp

From 0.26% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.26%

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< 1:140.15.0esr-1~deb12u1 | < 1:140.15.0esr-1~deb13u1 | < 1:153.2.0esr-1
Mozilla1 product
  • thunderbird< 140.15.0 | ≥ 141.0, < 153.2.0 | ≥ 154.0, < 155.0
Ubuntu1 product
  • thunderbirdAll versions (No fix recorded)

3 vendors · 3 products

References

8 links