CVE-2026-4371A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer.
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.
- CVSS
- 7.4 HIGH (v3.1, NVD)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
- Weakness (CWE)
- CWE-126, CWE-130
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Modified
- Record last updated
- Jul 15, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
mozilla thunderbird mozilla:thunderbird | before 140.9.0; before 149.0 | NVD |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2023493permissions-required
- https://www.mozilla.org/security/advisories/mfsa2026-23/vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2026-24/vendor-advisory
- https://access.redhat.com/errata/RHSA-2026:6188
- https://access.redhat.com/errata/RHSA-2026:6342
- https://access.redhat.com/errata/RHSA-2026:6917
- https://access.redhat.com/errata/RHSA-2026:8284
- https://access.redhat.com/errata/RHSA-2026:8285
- https://access.redhat.com/errata/RHSA-2026:8286
- https://access.redhat.com/errata/RHSA-2026:8287
- https://access.redhat.com/errata/RHSA-2026:8288
- https://access.redhat.com/errata/RHSA-2026:8289
- https://access.redhat.com/errata/RHSA-2026:8290
- https://access.redhat.com/errata/RHSA-2026:8315
- https://access.redhat.com/errata/RHSA-2026:8850
- https://access.redhat.com/security/cve/CVE-2026-4371
- https://bugzilla.redhat.com/show_bug.cgi?id=2451001
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4371.json
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.