CVE-2026-126135 mozilla thunderbird
mozilla thunderbird: no CVSS score yet. EPSS 0.2% estimated probability of exploitation activity in the next 30 days.
On this page
If an attacker was able to perform a man-in-the-middle attack on an SMTP or POP3 server connection using STARTTLS, the attacker could inject server responses before the TLS handshake completed. Thunderbird would process these responses after the handshake, as if they had been received from the server over the encrypted connection. This could be used to make Thunderbird report a different outcome for sending or fetching mail, and to show attacker-controlled text in error messages. The encrypted connection itself was not compromised, and credentials were not exposed. Connections using SSL/TLS instead of STARTTLS were not affected. This vulnerability was fixed in Thunderbird 160 and Thunderbird 153.7.
- EPSS
- 0.2% estimated probability of exploitation activity in the next 30 days; 8th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
- Published
- Modified
- Assigned by
- mozilla (CNA)
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
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Affected
Versions
From the CNA's record in the CVE List.
Fixed in
| Product | Release line | Fixed in |
|---|---|---|
| Mozilla Thunderbird | 153 | 153.7 |
| Mozilla Thunderbird | later releases | 160 |
Fix and patched versions
- Mozilla Thunderbird: fixed in 153.7
- Mozilla Thunderbird: fixed in 160
- Debian: fixed package versions per release
Linux distributions
| Distribution | Release | Package | Fixed in | Advisory |
|---|---|---|---|---|
| Debian | 12 | thunderbird | 1:153.7.0esr-1~deb12u1 | DEBIAN-CVE-2026-126135 |
| Debian | 13 | thunderbird | 1:153.7.0esr-1~deb13u1 | DEBIAN-CVE-2026-126135 |
| Debian | 14 | thunderbird | no fix listed | DEBIAN-CVE-2026-126135 |
| Ubuntu | 22.04:LTS, 24.04:LTS, 26.04:LTS and 1 more | thunderbird | no fix listed | UBUNTU-CVE-2026-126135 |
From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.