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[USN-8486-1] libssh2 vulnerabilities

Posted on 30 June 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8486-1
June 30, 2026

libssh2 vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.04 LTS
- Ubuntu 25.10
- Ubuntu 24.04 LTS

Summary:

Several security issues were fixed in libssh2.

Software Description:
- libssh2: Client-side C library implementing the SSH2 protocol

Details:

It was discovered that libssh2 incorrectly handled the sftp_symlink()
function. A malicious SSH server or machine-in-the-middle attacker could
possibly use this issue to obtain sensitive information or cause a denial
of service. (CVE-2025-15661)

It was discovered that libssh2 had a pre-authentication denial of service
vulnerability in the SSH_MSG_EXT_INFO handler. A malicious SSH server could
possibly use this issue to cause a client CPU exhaustion loop, resulting in
a denial of service. (CVE-2026-55199)

It was discovered that libssh2 incorrectly handled packet length fields. A
remote attacker could possibly use this issue to execute arbitrary code.
This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS.
(CVE-2026-55200)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 26.04 LTS
libssh2-1t64 1.11.1-1ubuntu0.26.04.2

Ubuntu 25.10
libssh2-1t64 1.11.1-1ubuntu0.25.10.2

Ubuntu 24.04 LTS
libssh2-1t64 1.11.0-4.1ubuntu0.24.04.2

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-8486-1
CVE-2025-15661, CVE-2026-55199, CVE-2026-55200

Package Information:
https://launchpad.net/ubuntu/+source/libssh2/1.11.1-1ubuntu0.26.04.2
https://launchpad.net/ubuntu/+source/libssh2/1.11.1-1ubuntu0.25.10.2
https://launchpad.net/ubuntu/+source/libssh2/1.11.0-4.1ubuntu0.24.04.2

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