CVE-2026-42392 in Dovecot Pro
Summary
by MITRE • 08/28/2026
An attacker that has valid credentials can send an invalid IMAP URLFETCH command, which causes uninitialized memory to be included in the error response returned to the client. Process memory contents can be disclosed to the client, which may include sensitive data. Disable the IMAP URLAUTH functionality. Update to non-vulnerable version. No publicly available exploits are known.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability described involves a critical information disclosure flaw within an email server's implementation of the Internet Message Access Protocol (IMAP), specifically affecting the URLFETCH command processing logic. This issue arises when an authenticated attacker, possessing valid credentials for the mail system, submits a malformed or invalid IMAP URLFETCH request to the server. Instead of handling this input error gracefully by returning a standard protocol-level error message that clearly indicates the syntax violation, the vulnerable software fails to properly initialize certain memory buffers before attempting to construct the response payload. This lack of proper initialization leads to the inclusion of uninitialized stack or heap memory in the data returned to the client as part of the error response body.
From a technical perspective, this flaw represents a classic instance of an out-of-bounds read or use-after-free scenario where the application reads from memory locations that have not been explicitly zeroed or allocated for the specific purpose of holding the error message content. In many server-side applications, particularly those written in languages like C or C++, uninitialized variables may retain data from previous operations performed by other users or system processes within the same process space. Consequently, when this raw memory is transmitted back to the attacker via the IMAP response stream, it effectively leaks sensitive internal state information. This can include cryptographic keys, session tokens, passwords of other users, private email content, or even kernel-level data depending on how the server manages its memory and privilege levels.
The operational impact of this vulnerability is significant due to the potential for cascading security breaches. While the initial disclosure provides raw memory dumps, these fragments often contain high-value targets such as authentication cookies or session identifiers that can be hijacked by an attacker to impersonate legitimate users without needing their passwords. Furthermore, exposure of internal application logic or database query structures could facilitate further exploitation attempts against other components of the infrastructure. The requirement for valid credentials means this is not a remote unauthenticated attack but rather requires initial access through compromised accounts or social engineering tactics to gain entry into the mail system before the vulnerability can be triggered.
In terms of industry classification, this flaw aligns with CWE-200: Information Exposure and CWE-457: Use of Uninitialized Variable within the Common Weakness Enumeration framework. It also maps to MITRE ATT&CK technique T1005: Data from Local System Retrieval under the Collection tactic, as it involves extracting data directly from the memory space of a running process on the target system. The ability to read arbitrary memory locations is often a precursor to more advanced exploitation techniques such as return-oriented programming or bypassing address space layout randomization protections in subsequent attack chains.
Mitigation strategies should focus primarily on patch management and configuration hardening. Organizations must immediately update their email server software to versions where this specific IMAP URLFETCH handling logic has been corrected, ensuring that all error responses are strictly sanitized and do not include uninitialized memory buffers. In environments where immediate patching is not feasible due to compatibility or testing constraints, disabling the IMAP URLAUTH functionality serves as an effective compensating control since it removes the attack vector entirely by preventing clients from issuing the vulnerable command type. Additionally, implementing strict input validation on all IMAP commands and ensuring that error handling routines explicitly zero out memory buffers before use can prevent similar issues in other parts of the application stack. Regular security audits and penetration testing should be conducted to verify that no residual uninitialized data leaks occur during normal operation or under stress conditions involving malformed inputs from authenticated users.