Bug 2556405 (CVE-2026-113868)

Summary: CVE-2026-113868 thunderbird: Thunderbird: information disclosure via malformed authentication challenge
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: gotiwari, jhorak, mvyas, rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Thunderbird. When authenticating to an email server using NT LAN Manager (NTLM) or Generic Security Services Application Program Interface (GSSAPI), the client fails to properly validate the server's authentication challenge format. A malicious server can exploit this flaw by sending a specially crafted challenge, causing Thunderbird to return uninitialized memory and leading to information disclosure. A malformed challenge can also trigger an out-of-bounds read that crashes the client, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-10-20 19:31:48 UTC 
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.