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Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS : OpenSSH vulnerabilities (USN-8804-1)

high Nessus Plugin ID 349265

Synopsis

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

Description

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8804-1 advisory.

 Florian Kohnhuser discovered that OpenSSH incorrectly handled shell metacharacters in certain usernames.
 An attacker could possibly use this issue to execute arbitrary commands when certain non-default configurations were used, resulting in arbitrary code execution. This issue only affected Ubuntu 14.04 LTS. (CVE-2026-35386)

 Christos Papakonstantinou discovered that OpenSSH incorrectly handled ECDSA algorithm restrictions. An attacker could possibly use this issue to cause unintended ECDSA algorithms to be accepted, resulting in security restrictions being bypassed. (CVE-2026-35387)

 Vladimir Tokarev discovered that OpenSSH incorrectly handled certain principal restrictions in authorized_keys files. An attacker could possibly use this issue to bypass principal restrictions, resulting in unauthorized access. This issue only affected Ubuntu 14.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS. (CVE-2026-35414)

 It was discovered that OpenSSH incorrectly handled downloaded file paths when using sftp with an untrusted server. An attacker could possibly use this issue to write downloaded files outside the intended location, resulting in unauthorized file modification. (CVE-2026-59995)

 It was discovered that OpenSSH incorrectly handled command-line arguments in internal-sftp. An attacker could possibly use this issue to cause certain security-related arguments to be ignored, resulting in security restrictions being bypassed. (CVE-2026-59997)

 It was discovered that OpenSSH incorrectly handled GSSAPIStrictAcceptorCheck when used with Windows Active Directory. An attacker could possibly use this issue to bypass GSSAPI security restrictions, resulting in unauthorized access. (CVE-2026-59998)

 It was discovered that OpenSSH incorrectly handled forwarding restrictions when DisableForwarding and PermitTunnel were used together. An attacker could possibly use this issue to create tunnels despite forwarding being disabled, resulting in security restrictions being bypassed. This issue only affected Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2026-59999)

 It was discovered that OpenSSH incorrectly handled authentication attempt limits when using GSSAPI authentication. An attacker could possibly use this issue to consume excessive system resources, resulting in a denial of service. (CVE-2026-60000)

 It was discovered that OpenSSH did not always enforce the minimum authentication delay. An attacker could possibly use this issue to perform authentication attempts more rapidly than intended, resulting in weakened brute-force protections. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-60001)

 It was discovered that OpenSSH incorrectly handled certain concurrent remote forwarding operations. An attacker could possibly use this issue to trigger a use-after-free, resulting in a denial of service or arbitrary code execution. (CVE-2026-73282)

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-8804-1

Plugin Details

Severity: High

ID: 349265

File Name: ubuntu_USN-8804-1.nasl

Version: 1.1

Type: Local

Agent: unix

Published: 9/23/2026

Updated: 9/23/2026

Supported Sensors: Nessus Agent, Continuous Assessment, Nessus

Risk Information

VPR

Risk Factor: High

Score: 7.6

Percentile: 98.46

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 5.8

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

CVSS Score Source: CVE-2026-59999

CVSS v3

Risk Factor: High

Base Score: 8.1

Temporal Score: 7.1

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

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

CVSS Score Source: CVE-2026-35414

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:14.04:-:lts, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:openssh-client-ssh1, p-cpe:/a:canonical:ubuntu_linux:openssh-client, 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-krb5, 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: 9/22/2026

Vulnerability Publication Date: 4/2/2026

Reference Information

CVE: CVE-2026-35386, CVE-2026-35387, CVE-2026-35414, CVE-2026-59995, CVE-2026-59997, CVE-2026-59998, CVE-2026-59999, CVE-2026-60000, CVE-2026-60001, CVE-2026-73282

IAVA: 2026-A-0296-S, 2026-A-0691-S, 2026-A-0847

USN: 8804-1