CVE-2026-40016

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.

Published: 2026-05-12 Last update: 2026-05-18 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40016 is rated Low Risk (21.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-40016

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-13 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40016

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.6 3.6 [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2026-40016

GitHub Security Advisory for CVE-2026-40016

GHSA-m97m-74mq-mqc6 · Severity: medium — Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass...

OS Trackers for CVE-2026-40016

vendor priority summary link
debian not yet assigned CVE-2026-40016 not yet assigned priority: Debian including 1 source packages (dovecot), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2026-40016
suse medium CVE-2026-40016 severity moderate: SUSE including 1 source package names (dovecot), 19 product×package rows across 19 product lines (SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS, … (19 product lines)): Known Not Affected 19. https://www.suse.com/security/cve/CVE-2026-40016/
ubuntu medium CVE-2026-40016 medium priority: Ubuntu including 1 source packages (dovecot), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needs-triage 5, released 4. https://ubuntu.com/security/CVE-2026-40016

Affected software / configurations for CVE-2026-40016

Vendor Product Version Raw CPE
dovecot dovecot < 2.4.4 cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:*
open-xchange dovecot < 3.1.5 cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*

References for CVE-2026-40016

cvelogic Threat Intelligence