CVE-2026-47088 in Cyrus IMAP
Summary
by MITRE • 07/16/2026
An issue was discovered in cyrus-imapd in Cyrus IMAP through 3.12.2. There is heap exposure in nested MIME comment parsing. An authenticated IMAP user could craft an email message containing an RFC 822 comment ending with a backslash. When parsing the message, the server would read past the message's end in memory, and read into the heap, returning the read content to the user.
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Analysis
by VulDB Data Team • 07/16/2026
This vulnerability exists within the Cyrus IMAP server software version 3.12.2 and earlier, specifically in how the system handles nested MIME comment parsing during email message processing. The flaw manifests when an authenticated user constructs a malicious email message containing an RFC 822 formatted comment that concludes with a backslash character. This particular formatting triggers a heap memory exposure condition where the parsing routine fails to properly bounds-check memory access, causing the server to read beyond the allocated buffer boundaries into adjacent heap memory regions.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the IMAP message parser component. When the server encounters the malformed comment structure with trailing backslash, the parsing algorithm incorrectly calculates buffer boundaries and continues reading memory locations that extend past the legitimate message data. This heap over-read behavior allows an attacker to potentially extract sensitive information from the server's memory space including potentially confidential data, session tokens, or other system-related information that may be stored in adjacent heap allocations.
The operational impact of this vulnerability is significant for organizations relying on Cyrus IMAP servers for email services. An authenticated attacker with valid IMAP credentials can exploit this weakness by simply sending a specially crafted email message to any mailbox on the affected server. Upon processing this malicious message, the server's response will inadvertently include portions of heap memory contents in the returned data, effectively leaking information that could aid in further attacks or compromise system integrity. This vulnerability directly maps to CWE-125: Out-of-bounds Read and can be classified under ATT&CK technique T1074.001: Data Staged for Exfiltration, as it enables unauthorized access to memory contents through legitimate server operations.
Mitigation strategies should focus on immediate software updates to Cyrus IMAP versions 3.12.3 or later where this vulnerability has been patched. Organizations should also implement network-level monitoring to detect unusual patterns in IMAP traffic that might indicate exploitation attempts. Additionally, administrators should consider implementing access controls and limiting the scope of authenticated users who can submit arbitrary email content to critical mailboxes. The patch addresses the core memory handling issue by introducing proper bounds checking in the comment parsing logic and ensuring that all memory accesses remain within legitimate buffer boundaries.