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Fencer Intel
high 7.5

CVE-2026-27857 json

Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage.

published 7mo ago modified 14d ago also EUVD-2026-16567

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 52%
public exploits
0
none known

Summary

Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. No publicly available exploits are known.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 1:2.3.21-16.el10_1.1, 1:2.3.21-19.el10_2
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support 1:2.3.21-16.el10_0.1
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support 1:2.2.36-8.el7_9.1
  • Red Hat Red Hat Enterprise Linux 8 1:2.3.16-7.el8_10
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 1:2.3.8-9.el8_4.1
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 1:2.3.8-9.el8_4.1
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 1:2.3.16-2.el8_6.1
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service 1:2.3.16-2.el8_6.1
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions 1:2.3.16-2.el8_6.1
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service 1:2.3.16-3.el8_8.1
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions 1:2.3.16-3.el8_8.1
  • Red Hat Red Hat Enterprise Linux 9 1:2.3.16-15.el9_7.1, 1:2.3.16-18.el9_8
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions 1:2.3.16-3.el9_0.1
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions 1:2.3.16-8.el9_2.2
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support 1:2.3.16-11.el9_4.2
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support 1:2.3.16-15.el9_6.1
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u2
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u4
  • dovecot Debian 14 1:2.4.3+dfsg1-1

debian advisories DEBIAN-CVE-2026-27857

  • dovecot Ubuntu 22.04 LTS 1:2.3.16+dfsg1-3ubuntu2.7
  • dovecot Ubuntu 24.04 LTS 1:2.3.21+dfsg1-2ubuntu6.3
  • dovecot Ubuntu 25.10 1:2.4.1+dfsg1-5ubuntu4.1

ubuntu advisories UBUNTU-CVE-2026-27857

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • dovecot RHEL 9 1:2.3.16-18.el9_8
  • dovecot-mysql RHEL 9 1:2.3.16-18.el9_8
  • dovecot-pgsql RHEL 9 1:2.3.16-18.el9_8
  • dovecot-pigeonhole RHEL 9 1:2.3.16-18.el9_8
  • dovecot RHEL 10.2 1:2.3.21-19.el10_2
  • dovecot-mysql RHEL 10.2 1:2.3.21-19.el10_2
  • dovecot-pgsql RHEL 10.2 1:2.3.21-19.el10_2
  • dovecot-pigeonhole RHEL 10.2 1:2.3.21-19.el10_2

red hat advisories RHSA-2026:26564RHSA-2026:19455RHSA-2026:19453RHSA-2026:19364RHSA-2026:19149RHSA-2026:18053

  • dovecot23 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 2.3.21.1-150200.76.1
  • dovecot24 SLES for SAP applications 16.0, SLES 16.0 2.4.3-160000.1.1

suse advisories SUSE-SU-2026:4139-1SUSE-SU-2026:21208-1

  • dovecot24 openSUSE Leap 16.0 2.4.3-160000.1.1
  • dovecot24 openSUSE Tumbleweed 2.4.3-1.1

opensuse advisories openSUSE-SU-2026:20554-1openSUSE-SU-2026:10442-1

  • dovecot AlmaLinux 10 1:2.3.21-19.el10_2
  • dovecot-mysql AlmaLinux 10 1:2.3.21-19.el10_2
  • dovecot-pgsql AlmaLinux 10 1:2.3.21-19.el10_2
  • dovecot-pigeonhole AlmaLinux 10 1:2.3.21-19.el10_2
  • dovecot AlmaLinux 9 1:2.3.16-18.el9_8
  • dovecot-mysql AlmaLinux 9 1:2.3.16-18.el9_8
  • dovecot-pgsql AlmaLinux 9 1:2.3.16-18.el9_8
  • dovecot-pigeonhole AlmaLinux 9 1:2.3.16-18.el9_8

almalinux advisories ALSA-2026:19149ALSA-2026:19364ALSA-2026:13830ALSA-2026:13857ALSA-2026:13498

  • dovecot Rocky Linux 10 1:2.3.21-19.el10_2
  • dovecot Rocky Linux 9 1:2.3.16-18.el9_8
  • dovecot Rocky Linux 9 1:2.3.16-15.el9_7.1
  • dovecot Rocky Linux 8 1:2.3.16-7.el8_10
  • dovecot Rocky Linux 10 1:2.3.21-16.el10_1.1

rocky linux advisories RLSA-2026:19149RLSA-2026:19364RLSA-2026:13857RLSA-2026:13830RLSA-2026:13498

  • dovecot Alpine 3.24, Alpine 3.23 2.4.3-r0

alpine advisories ALPINE-CVE-2026-27857

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-27857 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-27857 updated cvss 7.5

dovecot: denial of service via specially crafted NOOP command

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix planned “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.”
  • Red Hat CodeReady Linux Builder EUS (v.9.4) dovecot 2.3.16-11.el9_4.2
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17625
  • Red Hat CodeReady Linux Builder EUS (v.9.6) dovecot 2.3.16-15.el9_6.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17626
  • Red Hat Enterprise Linux AppStream (v. 8) dovecot 2.3.16-7.el8_10, dovecot-mysql 2.3.16-7.el8_10, dovecot-pgsql 2.3.16-7.el8_10, dovecot-pigeonhole 2.3.16-7.el8_10
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13830
  • Red Hat Enterprise Linux AppStream (v. 9) dovecot 2.3.16-18.el9_8, dovecot 2.3.16-15.el9_7.1, dovecot-mysql 2.3.16-18.el9_8, dovecot-pgsql 2.3.16-18.el9_8, dovecot-mysql 2.3.16-15.el9_7.1, dovecot-pgsql 2.3.16-15.el9_7.1, +2 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13857
  • Red Hat Enterprise Linux AppStream (v. 10) dovecot 2.3.21-19.el10_2, dovecot 2.3.21-16.el10_1.1, dovecot-mysql 2.3.21-19.el10_2, dovecot-pgsql 2.3.21-19.el10_2, dovecot-mysql 2.3.21-16.el10_1.1, dovecot-pgsql 2.3.21-16.el10_1.1, +2 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13498
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) dovecot 2.3.8-9.el8_4.1, dovecot-mysql 2.3.8-9.el8_4.1, dovecot-pgsql 2.3.8-9.el8_4.1, dovecot-pigeonhole 2.3.8-9.el8_4.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:19455
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) dovecot 2.3.16-2.el8_6.1, dovecot-mysql 2.3.16-2.el8_6.1, dovecot-pgsql 2.3.16-2.el8_6.1, dovecot-pigeonhole 2.3.16-2.el8_6.1 Red Hat Enterprise Linux AppStream E4S (v.8.6) dovecot 2.3.16-2.el8_6.1, dovecot-mysql 2.3.16-2.el8_6.1, dovecot-pgsql 2.3.16-2.el8_6.1, dovecot-pigeonhole 2.3.16-2.el8_6.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:19453
show 14 more
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) dovecot 2.3.16-3.el8_8.1, dovecot-mysql 2.3.16-3.el8_8.1, dovecot-pgsql 2.3.16-3.el8_8.1, dovecot-pigeonhole 2.3.16-3.el8_8.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:18053
  • Red Hat Enterprise Linux AppStream E4S (v.9.0) dovecot 2.3.16-3.el9_0.1, dovecot-mysql 2.3.16-3.el9_0.1, dovecot-pgsql 2.3.16-3.el9_0.1, dovecot-pigeonhole 2.3.16-3.el9_0.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17630
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) dovecot 2.3.16-8.el9_2.2, dovecot-mysql 2.3.16-8.el9_2.2, dovecot-pgsql 2.3.16-8.el9_2.2, dovecot-pigeonhole 2.3.16-8.el9_2.2
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17628
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) dovecot 2.3.21-16.el10_0.1, dovecot-mysql 2.3.21-16.el10_0.1, dovecot-pgsql 2.3.21-16.el10_0.1, dovecot-pigeonhole 2.3.21-16.el10_0.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17602
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) dovecot 2.3.16-11.el9_4.2, dovecot-mysql 2.3.16-11.el9_4.2, dovecot-pgsql 2.3.16-11.el9_4.2, dovecot-pigeonhole 2.3.16-11.el9_4.2
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17625
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) dovecot 2.3.16-15.el9_6.1, dovecot-mysql 2.3.16-15.el9_6.1, dovecot-pgsql 2.3.16-15.el9_6.1, dovecot-pigeonhole 2.3.16-15.el9_6.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17626
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) dovecot 2.3.8-9.el8_4.1, dovecot-mysql 2.3.8-9.el8_4.1, dovecot-pgsql 2.3.8-9.el8_4.1, dovecot-pigeonhole 2.3.8-9.el8_4.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:19455
  • Red Hat Enterprise Linux AppStream TUS (v.8.6) dovecot 2.3.16-2.el8_6.1, dovecot-mysql 2.3.16-2.el8_6.1, dovecot-pgsql 2.3.16-2.el8_6.1, dovecot-pigeonhole 2.3.16-2.el8_6.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:19453
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) dovecot 2.3.16-3.el8_8.1, dovecot-mysql 2.3.16-3.el8_8.1, dovecot-pgsql 2.3.16-3.el8_8.1, dovecot-pigeonhole 2.3.16-3.el8_8.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:18053
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) dovecot 2.3.16-18.el9_8, dovecot 2.3.16-15.el9_7.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13857
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) dovecot-devel 2.3.21-19.el10_2, dovecot-devel 2.3.21-16.el10_1.1, dovecot-debuginfo 2.3.21-19.el10_2, dovecot-debuginfo 2.3.21-16.el10_1.1, dovecot-debugsource 2.3.21-19.el10_2, dovecot-debugsource 2.3.21-16.el10_1.1, +6 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13498
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) dovecot-devel 2.3.21-16.el10_0.1, dovecot-debuginfo 2.3.21-16.el10_0.1, dovecot-debugsource 2.3.21-16.el10_0.1, dovecot-mysql-debuginfo 2.3.21-16.el10_0.1, dovecot-pgsql-debuginfo 2.3.21-16.el10_0.1, dovecot-pigeonhole-debuginfo 2.3.21-16.el10_0.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:17602
  • Red Hat Enterprise Linux CRB (v. 8) dovecot 2.3.16-7.el8_10
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:13830
  • Red Hat Enterprise Linux Server (v. 7 ELS) dovecot 2.2.36-8.el7_9.1, dovecot-mysql 2.2.36-8.el7_9.1, dovecot-pgsql 2.2.36-8.el7_9.1, dovecot-pigeonhole 2.2.36-8.el7_9.1 Red Hat Enterprise Linux Server Optional (v. 7 ELS) dovecot-devel 2.2.36-8.el7_9.1, dovecot-debuginfo 2.2.36-8.el7_9.1
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.” RHSA-2026:26564

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7mo ago

Exploit prediction

0.68% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Open-Xchange GmbH OX Dovecot Pro
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 6

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.