CVE-2025-26466

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

OpenSSH is the premier connectivity tool for remote login with the SSH protocol. \ It encrypts all traffic to eliminate eavesdropping, connection hijacking, and \ other attacks. In addition, OpenSSH provides a large suite of secure tunneling \ capabilities, several authentication methods, and sophisticated configuration options.

Security Fix(es):

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.(CVE-2025-26465)

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.(CVE-2025-26466)

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

These are all security issues fixed in the openssh-9.9p2-1.1 package on the GA media of openSUSE Tumbleweed.

This update for openssh fixes the following issues:

• CVE-2025-26465: Fixed MitM attack against OpenSSH's VerifyHostKeyDNS-enabled client (bsc#1237040).
• CVE-2025-26466: Fixed DoS attack against OpenSSH's client and server (bsc#1237041).

This update for openssh fixes the following issues:

• CVE-2025-26465: Fixed MitM attack against OpenSSH's VerifyHostKeyDNS-enabled client (bsc#1237040).
• CVE-2025-26466: Fixed DoS attack against OpenSSH's client and server (bsc#1237041).

Other bugfixes:

• Fix ssh client segfault with GSSAPIKeyExchange=yes in ssh_kex2 due to gssapi proposal not being correctly initialized (bsc#1236826).
• Add #include <stdlib.h> in some files added by the ldap patch to fix build with gcc14 (bsc#1225904).
• Added missing struct initializer, added missing parameter (bsc#1222840).
• Remove OPENSSL_HAVE_EVPGCM-ifdef, which is no longer supported by upstream (bsc#1221928).
• Use %config(noreplace) for sshd_config. In any case, it's recommended to drop a file in sshd_config.d instead of editing sshd_config (bsc#1221063).
• Add a patch to fix a regression introduced in 9.6 that makes X11 forwarding very slow (bsc#1229449).
• Drop keycat binary that is not supported, except of the code that is used by other SELinux patches (bsc#1229072).
• Fix RFC4256 implementation that keyboard-interactive authentication method can send instructions and sshd shows them to users (bsc#1229010).
• Add attempts to mitigate instances of secrets lingering in memory after a session exits (bsc#1186673, bsc#1213004, bsc#1213008).
• Remove empty line at the end of sshd-sle.pamd (bsc#1227456)

This update for openssh fixes the following issues:

Security issues fixed:

• CVE-2025-26465: Fixed a MitM attack against OpenSSH's VerifyHostKeyDNS-enabled client (bsc#1237040)
• CVE-2025-26466: Fixed a DoS attack against OpenSSH's client and server (bsc#1237041)

Other issues fixed:

• Fix ssh client segfault with GSSAPIKeyExchange=yes in ssh_kex2 due to gssapi proposal not being correctly initialized (bsc#1236826).
• Add a patch to fix a regression introduced in 9.6 that makes X11 forwarding very slow. (bsc#1229449)
• Fixed RFC4256 implementation so that keyboard-interactive authentication method can send instructions and sshd shows them to users even before a prompt is requested. This fixes MFA push notifications (bsc#1229010).
• Fix a dbus connection leaked in the logind patch that was missing a sd_bus_unref call
• Add a patch that fixes a small memory leak when parsing the subsystem configuration option:
• Remove empty line at the end of sshd-sle.pamd (bsc#1227456)

It was discovered that the OpenSSH client incorrectly handled the non-default VerifyHostKeyDNS option. If that option were enabled, an attacker could possibly impersonate a server by completely bypassing the server identity check. (CVE-2025-26465)

It was discovered that OpenSSH incorrectly handled the transport-level ping facility. A remote attacker could possibly use this issue to cause OpenSSH clients and servers to consume resources, leading to a denial of service. This issue only affected Ubuntu 24.04 LTS and Ubuntu 24.10. (CVE-2025-26466)