CVE-2026-113868: Uninitialized memory disclosure and out-of-bounds read in POP3 and SMTP NTLM authentication

Vulnerability summary

CVE-2026-113868 is a medium (CVSS 5.3) Out-of-bounds Read vulnerability in thunderbird. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 36.8% of scored vulnerabilities.

Timeline

1. 20-10-2026
   PublishedVulnerability first disclosed.
2. 20-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.