High 7.5Published Jul 22, 2026

CVE-2026-14899Off-by-one out of bounds read in MIME header parser for forwarding

Updated under an hour ago (Oct 26, 2026, 6:30 AM ET)

Does this affect you?

It affects Mozilla Thunderbird. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Do this next

Start free and add your stack

Free account, 1 product

Every CVE for Mozilla Thunderbird

Exploited in the last 30 days

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: 7.5 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness (CWE): CWE-193
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Analyzed
Record last updated: Jul 27, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Thunderbird mozilla:thunderbird (from the name)	140.13 builds before 140.* not affected; from 153 not affected	CNA record
mozilla thunderbird mozilla:thunderbird	before 140.13.0	NVD

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2046137permissions-required
https://www.mozilla.org/security/advisories/mfsa2026-71/vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-72/vendor-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.