CVE-2026-42006: An attacker can cause uncontrolled memory usage with excessive bracing over IMAP

Q: How do I fix CVE-2026-42006?

dovecot: upgrade to 2.4.4; dovecot: upgrade to 3.1.5. Exact commands for each OS are on this page.

Q: Is CVE-2026-42006 being exploited?

CVE-2026-42006 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-42006 affect?

CVE-2026-42006 affects dovecot, dovecot. Severity is medium (CVSS 4.3). An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left open. In particular, the fix was for closin

Q: How urgent is CVE-2026-42006?

Priority 27/100. No elevated risk signals yet.

Routine

MEDIUM 4.3UPGRADEUPGRADE

CVE-2026-42006 is a medium-severity flaw (CVSS 4.3) affecting dovecot, dovecot. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left open. In particular, the fix was for closing braces, but you could still use open braces to bypass the limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install fixed version, or configure vsz_limit for imap

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.6% (top 51%)
CISA exploited list	No
Weakness	CWE-400, CWE-770
Published	2026-05-12
Last modified	2026-10-26

Publisher (CNA): Open-Xchange · Vendor: dovecot · open-xchange

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-12 14:17 UTCPublished CVE record published
2026-10-26 18:10 UTCUpdated Record last modified

dovecot dovecot UPGRADE

Affected: < 2.4.4

Fixed in: 2.4.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy dovecot || rpm -q dovecot || dovecot --version

2. UPGRADE to 2.4.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade dovecot

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade dovecot

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

open-xchange dovecot UPGRADE

Affected: < 3.1.5

Fixed in: 3.1.5

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy dovecot || rpm -q dovecot || dovecot --version

2. UPGRADE to 3.1.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade dovecot

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade dovecot

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:41905] Important: dovecot security update 2026-07-22

Verify at the official source NVD · CVE Program · Report a problem with this page
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-2026-42006?

dovecot: upgrade to 2.4.4; dovecot: upgrade to 3.1.5. Exact commands for each OS are on this page.

Is CVE-2026-42006 being exploited?

CVE-2026-42006 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-2026-42006 affect?

CVE-2026-42006 affects dovecot, dovecot. Severity is medium (CVSS 4.3). An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left open. In particular, the fix was for closin

How urgent is CVE-2026-42006?

Priority 27/100. No elevated risk signals yet.

Software pages

Dovecot vulnerabilities

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

References

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