Red Hat Security Advisory: libssh security update

Fixed packages 5

Vulnerabilities 11

• High 8.8
  CVE-2026-59851

  Libssh: libssh: authentication bypass via missing gssapi principal check

  A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Alpine Wolfi
  Jul 21, 2026
• Medium 6.7
  CVE-2026-15370

  Libssh: libssh: stack buffer overflow in sftp server longname construction

  A flaw was found in libssh. During SFTP server directory listing, the longname field is constructed with unsafe concatenation into a fixed-size stack buffer. When a client causes the server to list attacker-controlled filenames, sufficiently long names can ov…

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Alpine Wolfi
  Jul 21, 2026
• Medium 6.5
  CVE-2026-59843

  Libssh: libssh: denial of service via zero advertised channel packet size

  A flaw was found in libssh. A remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Medium 6.5
  CVE-2026-59844

  Libssh: libssh: denial of service via oversized sftp read length

  A flaw was found in libssh. A remote authenticated client can issue SSH_FXP_READ requests with an arbitrarily large length, causing a libssh SFTP server to allocate excessive memory and potentially exhaust it through repeated requests.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Medium 5.9
  CVE-2026-59847

  Libssh: libssh: integrity downgrade via openssl aes-gcm tag verification

  A flaw was found in libssh. Incorrect AES-GCM finalization checks in builds using the OpenSSL backend can effectively remove integrity protection, allowing an in-path attacker to modify plaintext on the wire without detection.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Medium 5.3
  CVE-2026-59845

  Libssh: libssh: denial of service via unchecked proxycommand fork() failure

  A flaw was found in libssh. When ProxyCommand is used, an unchecked fork() failure can be stored as process ID -1; during cleanup, signals may then be sent across the caller's accessible process tree, leading to local denial of service.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Medium 5.3
  CVE-2026-59848

  Libssh: libssh: denial of service via sftp responses with unknown request ids

  A flaw was found in libssh. A malicious SFTP server can send responses for unknown request IDs that libssh clients keep queued indefinitely, causing unbounded memory growth and client-side denial of service.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Medium 4.3
  CVE-2026-59850

  Libssh: libssh: use-after-free via data callbacks on closed channels

  A flaw was found in libssh. If data packets are processed after a channel is closed, channel data callbacks can be invoked after the associated data has already been freed, leading to crashes or possible use-after-free conditions.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Azure Linux Alpine Wolfi
  Jul 21, 2026
• Low 3.9
  CVE-2026-59846

  Libssh: libssh: information disclosure via proxycommand %r username expansion

  A flaw was found in libssh. A malicious username expanded through %r in ProxyCommand handling can inject shell metacharacters, exposing environment variables and causing unintended shell behavior.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Alpine Wolfi
  Jul 21, 2026
• Low 3.7
  CVE-2026-59842

  Libssh: libssh: information disclosure via short gssapi curve25519 public key

  A flaw was found in libssh. During server-side GSSAPI key exchange, a client-supplied Curve25519 public key shorter than the expected length is copied without proper length validation, leading to an out-of-bounds heap read. This could allow a remote unauthent…

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Alpine Wolfi
  Jul 21, 2026
• Low 3.1
  CVE-2026-59849

  Libssh: libssh: denial of service via automatic certificate authentication loop

  A flaw was found in libssh. Logic errors in automatic certificate-based public key authentication can cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.

  Red Hat Red Hat Enterprise Linux 9 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 10 Linux Debian Ubuntu Alpine Wolfi
  Jul 21, 2026

References

• article
  https://access.redhat.com/security/updates/classification/#important
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498168
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498176
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498177
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498178
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498179
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498180
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498181
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498182
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498183
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2498184
• report
  https://bugzilla.redhat.com/show_bug.cgi?id=2499049
• advisory
  https://security.access.redhat.com/data/csaf/v2/advisories/2026/rhsa-2026_55855.json
• report
  https://access.redhat.com/security/cve/CVE-2026-15370
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-15370
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-15370
• report
  https://access.redhat.com/security/cve/CVE-2026-59842
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59842
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59842
• report
  https://access.redhat.com/security/cve/CVE-2026-59843
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59843
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59843
• report
  https://access.redhat.com/security/cve/CVE-2026-59844
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59844
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59844
• report
  https://access.redhat.com/security/cve/CVE-2026-59845
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59845
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59845
• report
  https://access.redhat.com/security/cve/CVE-2026-59846
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59846
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59846
• report
  https://access.redhat.com/security/cve/CVE-2026-59847
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59847
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59847
• report
  https://access.redhat.com/security/cve/CVE-2026-59848
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59848
• advisory
  https://nvd.nist.gov/vuln/detail/CVE-2026-59848
• report
  https://access.redhat.com/security/cve/CVE-2026-59849
• advisory
  https://www.cve.org/CVERecord?id=CVE-2026-59849