CVE-2026-42007 in Dovecot Pro
Summary
by MITRE • 08/28/2026
An attacker that has valid credentials can use a Sieve script with the editheader extension to trigger a use-after-free in the mail editing code, and to write memory contents beyond the intended buffer into the delivered mail. This causes memory leak and opportunity to do memory corruption during mail delivery, which can crash the delivery process and may allow execution of arbitrary code in the context of that process. Disable the Sieve editheader extension. 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 use-after-free condition within the mail editing functionality of an email system, specifically triggered by the utilization of the Sieve scripting language's editheader extension. This flaw allows an attacker who possesses valid credentials to craft and execute a malicious Sieve script that manipulates memory management operations incorrectly during the processing of incoming or outgoing messages. The core technical issue stems from improper handling of object lifecycles in the mail editing code, where references to freed memory blocks are retained and subsequently accessed. This leads to writes beyond the boundaries of intended buffers into delivered mail content, resulting in both a significant memory leak and opportunities for arbitrary memory corruption during the delivery process.
From an operational perspective, this vulnerability poses severe risks to system stability and security integrity. The immediate consequence is the potential crash of the mail delivery agent due to segmentation faults or other exceptions caused by invalid memory access patterns. However, the more critical risk lies in the possibility of remote code execution within the context of the affected process. By carefully crafting the malicious Sieve script, an attacker can exploit the use-after-free condition to overwrite function pointers or control data structures in memory, thereby gaining the ability to execute arbitrary commands with the privileges assigned to the mail delivery service account. This effectively compromises the confidentiality, integrity, and availability of the email infrastructure, potentially allowing further lateral movement within the network if the compromised process has access to sensitive resources.
In terms of industry standard classifications, this vulnerability aligns closely with CWE-416, which denotes Use After Free errors where a pointer is used after it has been freed, leading to undefined behavior and potential exploitation. Additionally, the attack vector relates to CWE-787, an out-of-bounds write that occurs when data is written beyond the allocated buffer limits due to improper validation or logic errors in memory management routines. From a tactical standpoint within the MITRE ATT&CK framework, this vulnerability facilitates techniques associated with Initial Access via valid credentials and Execution through script interpretation mechanisms like Sieve scripts, which are commonly used for automated mail processing but can be abused when input sanitization and resource lifecycle management are insufficiently enforced.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The most effective immediate countermeasure is to disable the Sieve editheader extension entirely if it is not strictly required for business operations, thereby removing the attack surface associated with this specific functionality. Organizations should also ensure that all software components are updated to non-vulnerable versions where patches have been officially released by the vendor. Furthermore, implementing strict least-privilege principles for mail delivery processes can limit the impact of a successful exploitation attempt. Regular auditing of Sieve scripts and enforcing rigorous input validation on script content before execution will help prevent similar vulnerabilities in future deployments. Continuous monitoring for anomalous memory usage patterns or unexpected crashes in mail services can also aid in early detection of potential exploitation attempts.