CVE-2026-110249 – A malicious, compromised, or MITM-controlled Exchange server can return a single well-form

A malicious, compromised, or MITM-controlled Exchange server can return a single well-formed SOAP response containing an element with enough attributes to keep Thunderbird’s main thread CPU-bound for seconds to hours. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.5.