# CVE-2026-113868: thunderbird: When authenticating to a POP3 or SMTP server using NTLM, Thunderbird did not check whether the server's challenge was...

CVE-2026-113868 is fixed in thunderbird on 1 platform, first by DEBIAN-CVE-2026-113868, released October 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-113868
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0043
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 20, 2026

## Description

When authenticating to a POP3 or SMTP server using NTLM, Thunderbird did not check whether the server's challenge was valid base64. A malicious server could send a challenge that caused Thunderbird to include uninitialized heap memory in its NTLM response, disclosing that memory to the server. A challenge consisting only of base64 padding also caused an out-of-bounds read, crashing Thunderbird. This affected accounts configured to use NTLM or GSSAPI authentication. The uninitialized memory disclosure only affected NTLM. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | thunderbird Debian 12.15 (bookworm) | 1:153.5.1esr-1~deb12u1 | [DEBIAN-CVE-2026-113868](https://patchblox.com/security/data/fix/linux/debian-cve-2026-113868.md) | Oct 27, 2026 |
| Linux | thunderbird Debian 13.5 (trixie) | 1:153.5.1esr-1~deb13u1 | [DEBIAN-CVE-2026-113868](https://patchblox.com/security/data/fix/linux/debian-cve-2026-113868.md) | Oct 27, 2026 |

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Data as of 2026-11-10T07:50:38Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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