Executive brief
Cyrus IMAP is an open-source email, contacts, and calendar server widely used in enterprises and universities. An authenticated user can craft a malicious JMAP blob request that reads beyond the bounds of an internal array, exposing sensitive heap memory data that should remain private.
Technical details
The vulnerability is an out-of-bounds read in the JMAP email-header blob ID handler. An authenticated attacker can craft a specially-formed blob ID of the form H<emailid>-<index> where the index parameter references an out-of-bounds memory location in the internal blob_headers array. During blob download, this causes the code to read past the end of the array, exposing adjacent heap memory. The vulnerability requires prior authentication and can be triggered via network. The fix is available in Cyrus IMAP version 3.12.4 and later.
Affected products
- Cyrus IMAP before 3.12.4
Timeline
- 2026-09-09: disclosed