CVE-2025-26465

Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled

Published Feb 18, 2025 CVSS 3.1 · 6.8 Medium EPSS 7.7% KEV · Not listed
Description
A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

Remediation

Vendor Workaround

This issue can be mitigated by disabling VerifyHostKeyDNS by setting that option to 'no' in an SSH client configuration file (such as /etc/ssh/ssh_config, ~/.ssh/config, or one of the files in the /etc/ssh/ssh_config.d/ directory). This is the default configuration in Red Hat Enterprise Linux. For configurations that require VerifyHostKeyDNS to be enabled (set to either 'yes' or 'ask'), mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4057-1 openssh security update
Debian DSA Debian DSA DSA-5868-1 openssh security update
Ubuntu USN Ubuntu USN USN-7270-1 OpenSSH vulnerabilities
Ubuntu USN Ubuntu USN USN-7270-2 OpenSSH vulnerability
References
Link Providers
http://seclists.org/fulldisclosure/2025/Feb/18 cve-icon
http://seclists.org/fulldisclosure/2025/May/7 cve-icon
http://seclists.org/fulldisclosure/2025/May/8 cve-icon
https://access.redhat.com/errata/RHSA-2025:16823 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2025:3837 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2025:6993 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2025:8385 cve-icon cve-icon
https://access.redhat.com/security/cve/CVE-2025-26465 cve-icon cve-icon
https://access.redhat.com/solutions/7109879 cve-icon cve-icon
https://blog.qualys.com/vulnerabilities-threat-research/2025/02/18/qualys-tru-discovers-two-vulnerabilities-in-openssh-cve-2025-26465-cve-2025-26466 cve-icon
https://bugzilla.redhat.com/show_bug.cgi?id=2344780 cve-icon cve-icon
https://bugzilla.suse.com/show_bug.cgi?id=1237040 cve-icon
https://cert-portal.siemens.com/productcert/html/ssa-082556.html cve-icon
https://cert-portal.siemens.com/productcert/html/ssa-585531.html cve-icon
https://ftp.openbsd.org/pub/OpenBSD/patches/7.6/common/008_ssh.patch.sig cve-icon
https://lists.debian.org/debian-lts-announce/2025/02/msg00020.html cve-icon
https://lists.mindrot.org/pipermail/openssh-unix-announce/2025-February/000161.html cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2025-26465 cve-icon
https://seclists.org/oss-sec/2025/q1/144 cve-icon cve-icon cve-icon cve-icon
https://security-tracker.debian.org/tracker/CVE-2025-26465 cve-icon
https://security.netapp.com/advisory/ntap-20250228-0003/ cve-icon
https://ubuntu.com/security/CVE-2025-26465 cve-icon
https://www.cve.org/CVERecord?id=CVE-2025-26465 cve-icon
https://www.openssh.com/releasenotes.html#9.9p2 cve-icon
https://www.openwall.com/lists/oss-security/2025/02/18/1 cve-icon
https://www.openwall.com/lists/oss-security/2025/02/18/4 cve-icon
https://www.theregister.com/2025/02/18/openssh_vulnerabilities_mitm_dos/ cve-icon
https://www.vicarius.io/vsociety/posts/cve-2025-26465-detect-vulnerable-openssh cve-icon
https://www.vicarius.io/vsociety/posts/cve-2025-26465-mitigate-vulnerable-openssh cve-icon
History
Type Values Removed Values Added
First Time appeared Redhat rhel Els
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/a:redhat:enterprise_linux:10
cpe:/o:redhat:rhel_els:6
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat rhel Els
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:8 cpe:/a:redhat:enterprise_linux:8::appstream
cpe:/o:redhat:enterprise_linux:8::baseos
References
Type Values Removed Values Added
First Time appeared Redhat discovery
CPEs cpe:/a:redhat:discovery:1.14::el9
Vendors & Products Redhat discovery
References
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:10
Type Values Removed Values Added
CPEs cpe:/a:redhat:enterprise_linux:9
cpe:/o:redhat:enterprise_linux:9
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:9 cpe:/a:redhat:enterprise_linux:9::appstream
cpe:/o:redhat:enterprise_linux:9::baseos
References
Type Values Removed Values Added
CPEs cpe:/a:redhat:rhel_eus:9.4
Type Values Removed Values Added
First Time appeared Debian
Debian debian Linux
Netapp
Netapp active Iq Unified Manager
Netapp ontap
Openbsd
Openbsd openssh
Redhat openshift Container Platform
CPEs cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:vmware_vsphere:*:*
cpe:2.3:a:netapp:ontap:9:*:*:*:*:*:*:*
cpe:2.3:a:openbsd:openssh:*:*:*:*:*:*:*:*
cpe:2.3:a:openbsd:openssh:6.8:p1:*:*:*:*:*:*
cpe:2.3:a:openbsd:openssh:9.9:-:*:*:*:*:*:*
cpe:2.3:a:openbsd:openssh:9.9:p1:*:*:*:*:*:*
cpe:2.3:a:redhat:openshift_container_platform:4.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:12.0:*:*:*:*:*:*:*
cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*
Vendors & Products Debian
Debian debian Linux
Netapp
Netapp active Iq Unified Manager
Netapp ontap
Openbsd
Openbsd openssh
Redhat openshift Container Platform
Type Values Removed Values Added
First Time appeared Redhat rhel Eus
CPEs cpe:/a:redhat:rhel_eus:9.4::appstream
cpe:/o:redhat:rhel_eus:9.4::baseos
Vendors & Products Redhat rhel Eus
References
Type Values Removed Values Added
References
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.
Title Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled
First Time appeared Redhat
Redhat enterprise Linux
Redhat openshift
Weaknesses CWE-390
CPEs cpe:/a:redhat:openshift:4
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
Redhat openshift
References
Metrics cvssV3_1

{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N'}