Summary
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.
Fixed packages 3
| Release | Package | Fixed in |
|---|---|---|
| AlmaLinux · 10 | libssh | 0.12.0-3.el10_2 |
| AlmaLinux · 10 | libssh-config | 0.12.0-3.el10_2 |
| AlmaLinux · 10 | libssh-devel | 0.12.0-3.el10_2 |
Vulnerabilities 11
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High 8.8
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.
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Medium 6.7
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…
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Medium 6.5
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.
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Medium 6.5
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.
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Medium 5.9
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.
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Medium 5.3
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.
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Medium 5.3
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.
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Medium 4.3
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.
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Low 3.9
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.
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Low 3.7
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…
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Low 3.1
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.
References
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report
https://access.redhat.com/security/cve/CVE-2026-15370
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report
https://access.redhat.com/security/cve/CVE-2026-59842
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report
https://access.redhat.com/security/cve/CVE-2026-59843
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report
https://access.redhat.com/security/cve/CVE-2026-59844
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report
https://access.redhat.com/security/cve/CVE-2026-59845
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report
https://access.redhat.com/security/cve/CVE-2026-59846
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report
https://access.redhat.com/security/cve/CVE-2026-59847
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report
https://access.redhat.com/security/cve/CVE-2026-59848
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report
https://access.redhat.com/security/cve/CVE-2026-59849
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report
https://access.redhat.com/security/cve/CVE-2026-59850
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report
https://access.redhat.com/security/cve/CVE-2026-59851
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report
https://bugzilla.redhat.com/2498168
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report
https://bugzilla.redhat.com/2498176
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report
https://bugzilla.redhat.com/2498177
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report
https://bugzilla.redhat.com/2498178
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report
https://bugzilla.redhat.com/2498179
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report
https://bugzilla.redhat.com/2498180
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report
https://bugzilla.redhat.com/2498181
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report
https://bugzilla.redhat.com/2498182
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report
https://bugzilla.redhat.com/2498183
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report
https://bugzilla.redhat.com/2498184
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report
https://bugzilla.redhat.com/2499049
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advisory
https://errata.almalinux.org/10/ALSA-2026-55855.html