CVE-2026-42007

A flaw was found in Dovecot. An authenticated attacker can use a Sieve script with the editheader extension to trigger a use-after-free vulnerability in the mail editing code. This can lead to memory corruption, potentially crashing the mail delivery process and allowing for arbitrary code execution in the context of that process.

This flaw requires an attacker to authenticate with valid credentials before it can be exploited, and exploitation additionally depends on the Sieve editheader extension being enabled, which is not Dovecot's default configuration. Because the CVSS attack vector requires low-privileged authentication (PR:L) rather than unauthenticated remote access, and the confirmed impact is primarily memory corruption leading to a crash of the mail delivery process, this issue is rated Important rather than Critical. Disabling the Sieve editheader extension fully mitigates the vulnerability without requiring a package update.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this vulnerability, disable the Sieve editheader extension in the Dovecot configuration. After modifying the configuration, the Dovecot service must be restarted for the changes to take effect. Disabling this extension will remove its associated functionality.