high CVSS 8 EPSS 0.35%

CVE-2026-42007·Dovecot vulnerability

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.

Severity
high
Software
Dovecot
Fixed in
1:2.4.1+dfsg1-6+deb13u7
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.35% — higher than 26% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-42007 scores 8 on CVSS, so a successful attack would be serious — but at 0.35%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 1:2.4.1+dfsg1-6+deb13u7

Fixed in: 1:2.4.1+dfsg1-6+deb13u7

How to fix this CVE

Organizations running Dovecot must immediately update to version 1:2.4.1+dfsg1-6+deb13u7 or later to patch a critical use-after-free vulnerability in the Sieve editheader extension that can lead to memory corruption and potential code execution during mail delivery. If immediate patching is not possible, disable the Sieve editheader extension in your Dovecot configuration to eliminate the attack vector. This vulnerability requires valid authentication credentials, making it a risk primarily for environments with compromised or malicious user accounts.

sudo dnf update -y dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check the installed Dovecot version by running: dovecot --version
  2. Step 2: Verify if Sieve editheader extension is enabled by checking /etc/dovecot/conf.d/90-sieve.conf for the line 'sieve_extensions = +editheader' or similar configuration
  3. Step 3: Search mail delivery logs for use-after-free crashes or segmentation faults: grep -i 'segfault\|use-after-free' /var/log/mail.log /var/log/dovecot/deliver.log
  4. Step 4: After patching, confirm the version with dovecot --version and verify it shows 1:2.4.1+dfsg1-6+deb13u7 or later

FAQ

What is CVE-2026-42007?

CVE-2026-42007 is a use-after-free vulnerability in Dovecot's Sieve mail filtering engine that occurs when the editheader extension processes specially crafted scripts, allowing authenticated attackers to corrupt memory and potentially execute arbitrary code in the mail delivery process.

Is CVE-2026-42007 being actively exploited?

No, CVE-2026-42007 is not currently listed on the CISA Known Exploited Vulnerabilities catalog, and no public exploits have been disclosed.

What versions of Dovecot are affected by CVE-2026-42007?

All versions of Dovecot prior to 1:2.4.1+dfsg1-6+deb13u7 are affected. The vulnerability is patched in version 1:2.4.1+dfsg1-6+deb13u7 and later.

How do I check if my server is vulnerable to CVE-2026-42007?

Run 'dovecot --version' and compare the output to 1:2.4.1+dfsg1-6+deb13u7. If your version is older and the Sieve editheader extension is enabled (check /etc/dovecot/conf.d/90-sieve.conf), your server is vulnerable.

Does Defensia detect CVE-2026-42007?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-42007 will appear in your dashboard with remediation steps.

Related Dovecot CVEs

CVE-2026-73208CVSS 9An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2 token response does not contain a scope claim, the audience claim is used in its place and checked against the configured required scopes. These are different concepts, and the audience claim does not describe what a token is allowed to do. A token that grants no relevant permissions can be accepted because its intended recipient value happens to match a configured scope name, granting access that should have been denied. It also hides an identity provider misconfiguration where scopes are not being issued at all. Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-40018CVSS 9None None None No publicly available exploits are known.
CVE-2026-40019CVSS 9An unauthenticated attacker can send a truncated quoted argument to the ManageSieve login process, which makes it spin in an infinite loop consuming CPU. This can cause degradation or denial of service for Sieve script management, and repeated connections can consume all available CPU on the server. Monitor system for abnormal CPU usage and kill the offending process. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-33605CVSS 9An unauthenticated attacker can crash the ManageSieve login process by sending a small malformed command before authenticating. If running in high-security mode (default for community releases), only the attacker's own connection is terminated. If running in high-performance mode (default for Pro releases), all connections handled by the same managesieve-login process are terminated. Repeating the attack can cause denial of service for Sieve script management. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-42391CVSS 9An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

References

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