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Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS / Pro Realtime 22.04 LTS / Pro Realtime 24.04 LTS : OpenSSH vulnerabilities (USN-8721-1)

medium Nessus Plugin ID 344614

Synopsis

The remote Ubuntu host is missing one or more security updates.

Description

The remote Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS / Pro Realtime 22.04 LTS / Pro Realtime 24.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8721-1 advisory.

 It was discovered that OpenSSH's ssh-agent incorrectly handled interactions between agent locking and the [email protected] extension. A remote attacker with access to a forwarded agent connection could possibly use this issue to perform operations that should only be available locally, such as adding tokens or using keys. (CVE-2026-73281)

 It was discovered that OpenSSH's ssh client incorrectly handled concurrent remote-forwarding operations. A remote attacker could possibly use this issue to cause a use-after-free condition, resulting in a denial of service or the execution of arbitrary code. (CVE-2026-73282)

 It was discovered that OpenSSH's sshd server incorrectly applied the restrict keyword from authorized_keys to tunnel forwarding requests. A local attacker with an authorized key could possibly use this issue to bypass intended tunnel forwarding restrictions. (CVE-2026-73283)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Update the affected packages.

See Also

https://ubuntu.com/security/notices/USN-8721-1

Plugin Details

Severity: Medium

ID: 344614

File Name: ubuntu_USN-8721-1.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 9/10/2026

Updated: 9/10/2026

Supported Sensors: Nessus Agent, Continuous Assessment, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 2.1

Percentile: 7.92

CVSS v2

Risk Factor: Medium

Base Score: 4

Temporal Score: 3

Vector: CVSS2#AV:N/AC:H/Au:N/C:P/I:P/A:N

CVSS Score Source: CVE-2026-73282

CVSS v3

Risk Factor: Medium

Base Score: 4.8

Temporal Score: 4.2

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, cpe:/o:canonical:ubuntu_linux:26.04:-:lts, cpe:/o:canonical:ubuntu_linux:pro:-:lts, p-cpe:/a:canonical:ubuntu_linux:openssh-client-gssapi, p-cpe:/a:canonical:ubuntu_linux:openssh-client, p-cpe:/a:canonical:ubuntu_linux:openssh-server-gssapi, p-cpe:/a:canonical:ubuntu_linux:openssh-server, p-cpe:/a:canonical:ubuntu_linux:openssh-sftp-server, p-cpe:/a:canonical:ubuntu_linux:openssh-tests, p-cpe:/a:canonical:ubuntu_linux:ssh-askpass-gnome, p-cpe:/a:canonical:ubuntu_linux:ssh

Required KB Items: Host/cpu, Host/Debian/dpkg-l, Host/Ubuntu, Host/Ubuntu/release

Exploit Ease: No known exploits are available

Patch Publication Date: 9/3/2026

Vulnerability Publication Date: 8/11/2026

Reference Information

CVE: CVE-2026-73281, CVE-2026-73282, CVE-2026-73283

IAVA: 2026-A-0847

USN: 8721-1