RHSA-2026:55855 - Security Advisory

Topic

An update for libssh is now available for Red Hat Enterprise Linux 10.

Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

Description

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)
• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)
• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)
• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)
• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)
• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)
• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)
• libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)
• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)
• libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)
• libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Solution

For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

Affected Products

• Red Hat Enterprise Linux for x86_64 10 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 10.2 x86_64
• Red Hat Enterprise Linux for IBM z Systems 10 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 10.2 s390x
• Red Hat Enterprise Linux for Power, little endian 10 ppc64le
• Red Hat Enterprise Linux for Power, little endian - Extended Update Support 10.2 ppc64le
• Red Hat Enterprise Linux for ARM 64 10 aarch64
• Red Hat Enterprise Linux for ARM 64 - Extended Update Support 10.2 aarch64
• Red Hat Enterprise Linux for ARM 64 - 4 years of updates 10.2 aarch64
• Red Hat Enterprise Linux for IBM z Systems - 4 years of updates 10.2 s390x
• Red Hat Enterprise Linux for Power, little endian - 4 years of support 10.2 ppc64le
• Red Hat Enterprise Linux for x86_64 - 4 years of updates 10.2 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Life Cycle 10.2 x86_64
• Red Hat Enterprise Linux for ARM 64 - Extended Life Cycle 10.2 aarch64
• Red Hat Enterprise Linux for Power, little endian - Extended Life Cycle 10.2 ppc64le
• Red Hat Enterprise Linux for IBM z Systems - Extended Life Cycle 10.2 s390x

Fixes

• BZ - 2498168 - CVE-2026-59842 libssh: libssh: information disclosure via short GSSAPI Curve25519 public key
• BZ - 2498176 - CVE-2026-59843 libssh: libssh: denial of service via zero advertised channel packet size
• BZ - 2498177 - CVE-2026-59844 libssh: libssh: denial of service via oversized SFTP read length
• BZ - 2498178 - CVE-2026-59845 libssh: libssh: denial of service via unchecked ProxyCommand fork() failure
• BZ - 2498179 - CVE-2026-59846 libssh: libssh: information disclosure via ProxyCommand %r username expansion
• BZ - 2498180 - CVE-2026-59847 libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification
• BZ - 2498181 - CVE-2026-59848 libssh: libssh: denial of service via SFTP responses with unknown request IDs
• BZ - 2498182 - CVE-2026-59849 libssh: libssh: denial of service via automatic certificate authentication loop
• BZ - 2498183 - CVE-2026-59850 libssh: libssh: use-after-free via data callbacks on closed channels
• BZ - 2498184 - CVE-2026-59851 libssh: libssh: authentication bypass via missing GSSAPI principal check
• BZ - 2499049 - CVE-2026-15370 libssh: libssh: stack buffer overflow in SFTP server longname construction

CVEs

• CVE-2026-15370
• CVE-2026-59842
• CVE-2026-59843
• CVE-2026-59844
• CVE-2026-59845
• CVE-2026-59846
• CVE-2026-59847
• CVE-2026-59848
• CVE-2026-59849
• CVE-2026-59850
• CVE-2026-59851

References

• https://access.redhat.com/security/updates/classification/#important