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High 7.5Published Sep 1, 2026
CVE-2026-84640One byte overflow read in mail parser
Updated under an hour ago ()
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It affects Mozilla Thunderbird. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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
- 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-126
- 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
- Sep 2, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Mozilla Thunderbird mozilla:thunderbird (from the name) | 140.15 builds before 140.* not affected; 153.2 builds before 153.* not affected; from 155 not affected | CNA record |
mozilla thunderbird mozilla:thunderbird | before 140.15.0; from 141.0 before 153.2.0; from 154.0 before 155.0 | NVD |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2063964permissions-required
- https://www.mozilla.org/security/advisories/mfsa2026-86/vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2026-87/vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2026-88/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.