CVE-2026-14899: mozilla thunderbird Off-by-one Error
Vulnerability summary
CVE-2026-14899 is a high (CVSS 7.5) Off-by-one Error vulnerability in mozilla thunderbird. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18.5% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 14 · Related 3Timeline
- 22-07-2026PublishedVulnerability first disclosed.
- 27-07-2026Last modifiedVulnerability information updated.
Description
The code to parse MIME headers for display when forwarding a message (if the setting to view all headers was enabled) had an off-by-one error, allowing a single byte to be read from the memory after the buffer for the headers, and potentially crashing Thunderbird. This vulnerability was fixed in Thunderbird 153 and Thunderbird 140.13.
CVSS metrics
4 scores · 4 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS trend
Probability
0.27%
Chance of exploitation in the next 30 days
Percentile
19%
Versus all other CVEs
30-day change
0.00 pp
From 0.27% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Debian1 product
- thunderbird< 1:140.13.0esr-2~deb12u1 | < 1:140.13.0esr-2~deb13u1 | < 1:140.13.0esr-1
Mozilla1 product
- thunderbird< 140.13.0
Ubuntu1 product
- thunderbirdAll versions (No fix recorded)
3 vendors · 3 products
