Critical [CVE-2026-42007] Arbitrary Code Execution via Sieve editheader use-after-free
This critical-severity Red Hat Linux advisory covers CVE-2026-42007 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
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. Update to non-vulnerable version.
No publicly available exploits are known. A flaw was found in Dovecot.
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. Red Hat severity: Important — CVSS 9.1 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H).
Weakness: CWE-825.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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