PatchTheCVECVE-2026-40016: Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU ti
CVE-2026-40016 is a medium-severity flaw (CVSS 5.3) affecting dovecot, dovecot. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.
Why this priority
- No elevated risk signals yet
A fixed release or distro patch exists.
Risk facts
| CVSS score | 5.3 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | High |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 0.3% (top 73%) |
| CISA exploited list | No |
| Weakness | CWE-400 |
| Published | 2026-05-12 |
| Last modified | 2026-10-26 |
Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-40016?
dovecot: upgrade to 2.4.4; dovecot: upgrade to 3.1.5. Exact commands for each OS are on this page.
Is CVE-2026-40016 being exploited?
CVE-2026-40016 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-40016 affect?
CVE-2026-40016 affects dovecot, dovecot. Severity is medium (CVSS 5.3). Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass config
How urgent is CVE-2026-40016?
Priority 25/100. No elevated risk signals yet.
Software pages
Related CVEs
- CVE-2026-27855 MEDIUM 6.8 UPGRADE UPGRADE Dovecot OTP authentication is vulnerable to replay attack under specific conditions
- CVE-2026-27857 MEDIUM 4.3 UPGRADE UPGRADE Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage
- CVE-2026-27858 HIGH 7.5 UPGRADE UPGRADE Attacker can send a specifically crafted message before authentication that causes managesieve to allocate lar
- CVE-2026-24031 HIGH 7.7 UPGRADE UPGRADE Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin
- CVE-2026-27856 HIGH 7.4 UPGRADE UPGRADE Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack