CVE-2026-40016
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk27th percentile - higher than 27% of all known CVEs
Summary
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.
Risk Assessment
An attacker can exploit the limit bypass to degrade mail server performance, potentially leading to denial of service (DoS) for other users. This requires the ability to upload Sieve scripts.
Recommendation
Install the fixed version of the software. Alternatively, prevent direct access to Sieve scripts via ManageSieve or local access.
Other vulnerabilities in ManageSieve
See all- CVE-2026-27858High
A vulnerability in managesieve allows an attacker to send a specially crafted message before authentication, causing excessive memory allocation. This can crash the managesieve-login process and make the protocol unavailable.
- CVE-2025-59032High
A vulnerability in ManageSieve causes the service to crash when processing the AUTHENTICATE command with a literal as the SASL initial response. This can be exploited to repeatedly crash the service, making it unavailable for other users.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS