NVD / CVE Program· CNA OX

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

Noroxi assessment

Priority: Monitor (action score 26/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.33% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: dovecot (Alpine:v3.23) 2.4.4-r0; dovecot (Debian:12) 1:2.3.19.1+dfsg1-2.1+deb12u6; dovecot (Debian:13) 1:2.4.1+dfsg1-6+deb13u6.

Low priority for now. Upgrade to dovecot (Alpine:v3.23) 2.4.4-r0; dovecot (Debian:12) 1:2.3.19.1+dfsg1-2.1+deb12u6; dovecot (Debian:13) 1:2.4.1+dfsg1-6+deb13u6 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 6.5 · v3.1—No exploit Fix available

Denial of service

Published: May 12, 2026
Updated: Oct 26, 2026
EPSS: 0.3% · 27th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 6.5
CNA · OX: 5.3; 1.2 point gap

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
dovecot	dovecot	cpe:2.3:a:dovecot:dovecot
open-xchange	dovecot	cpe:2.3:a:open-xchange:dovecot

Using dovecot? Add it to your stack and be the first to know about CVEs like this one. (Email server)

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

dovecot dovecotbefore 2.4.4
open-xchange dovecotbefore 3.1.5

Versions reported by the vendor

Affected version ranges reported by the assigning authority (OX). Independent of NVD's CPE analysis and usually ahead of it.

Open-Xchange GmbH OX Dovecot Pro
- up to and including 2.3.0affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.23	dovecot	before 2.4.4-r0	2.4.4-r0
Debian:12	dovecot	before 1:2.3.19.1+dfsg1-2.1+deb12u6	1:2.3.19.1+dfsg1-2.1+deb12u6
Debian:13	dovecot	before 1:2.4.1+dfsg1-6+deb13u6	1:2.4.1+dfsg1-6+deb13u6
Debian:14	dovecot	before 1:2.4.4+dfsg1-1	1:2.4.4+dfsg1-1
openSUSE:Leap 16.0	dovecot24	before 2.4.4-160000.1.1	2.4.4-160000.1.1
openSUSE:Tumbleweed	dovecot24	before 2.4.4-1.1	2.4.4-1.1
SUSE:Linux Enterprise Module for Server Applications 15 SP7	dovecot23	before 2.3.21.1-150200.76.1	2.3.21.1-150200.76.1
SUSE:Linux Enterprise Server 16.0	dovecot24	before 2.4.4-160000.1.1	2.4.4-160000.1.1
SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5	dovecot22	before 2.2.31-19.43.1	2.2.31-19.43.1

Same product

dovecot: all records

Other highest-scoring records for the same primary product.

CVE-2019-11500In Dovecot before 2.2.36.4 and 2.3.x before 2.3.7.2 (and Pigeonhole before 0.5.7.2), protocol processing can fail for quoted strings.
58Plan
CVE-2020-7046lib-smtp in submission-login and lmtp in Dovecot 2.3.9 before 2.3.9.3 mishandles truncated UTF-8 data in command parameters, as demonstrated
45Plan
CVE-2016-8652The auth component in Dovecot before 2.2.27, when auth-policy is configured, allows a remote attackers to cause a denial of service (crash)
37Monitor

Published before and after this one in the same product

← EarlierCVE-2026-27851May 12, 2026 · When safe filter is used with variable expansion, all following pipelines on the same string are incorrectly interpreted as safe too, enabli
36Monitor
← EarlierCVE-2026-33603May 12, 2026 · Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding.
21Monitor
Later →CVE-2026-40020May 12, 2026 · Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even if imap_acl_allow_anyone=no.
17Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:dovecot	2.4.4-r0 · Alpine:v3.23	Package registry (OSV)
debian:dovecot	1:2.3.19.1+dfsg1-2.1+deb12u6 · Debian:12	Package registry (OSV)
opensuse:dovecot24	2.4.4-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
suse:dovecot22	2.2.31-19.43.1 · SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5	Package registry (OSV)
suse:dovecot23	2.3.21.1-150200.76.1 · SUSE:Linux Enterprise Module for Server Applications 15 SP7	Package registry (OSV)
suse:dovecot24	2.4.4-160000.1.1 · SUSE:Linux Enterprise Server 16.0	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-2785746 days apartSending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage.
30Monitor
CVE-2026-2785846 days apartAttacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory.
30Monitor
CVE-2026-2785946 days apartA mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU.
21Monitor
CVE-2026-420060 days apartAn attacker can cause uncontrolled memory usage with excessive bracing over IMAP.
17Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:46 PM UTC

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References

documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records