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: 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: use-after-free via data callbacks on closed channels (CVE-2026-59850)
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 · 8 | libssh | 0.9.6-17.el8_10 |
| AlmaLinux · 8 | libssh-config | 0.9.6-17.el8_10 |
| AlmaLinux · 8 | libssh-devel | 0.9.6-17.el8_10 |
Vulnerabilities 7
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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.
References
-
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-2026-59850
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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/2498183
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advisory
https://errata.almalinux.org/8/ALSA-2026-62218.html