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CVE-2016-1908: Openbsd Openssh: Improper Authentication

CVE-2016-1908 is rated critical with a CVSS v3.1 base score of 9.8 and affects Openbsd Openssh, along with 8 other products in NVD’s configuration data. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available.

Vulnerability description

The client in OpenSSH before 7.2 mishandles failed cookie generation for untrusted X11 forwarding and relies on the local X11 server for access-control decisions, which allows remote X11 clients to trigger a fallback and obtain trusted X11 forwarding privileges by leveraging configuration issues on this X11 server, as demonstrated by lack of the SECURITY extension on this X11 server.

Severity breakdown

CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
Attack complexity: Low. No special conditions; the attack can be repeated reliably.
Privileges required: None. No account or prior access is needed.
User interaction: None. No action from any user is needed.
Scope: Unchanged. Impact stays within the vulnerable component.
Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-287: Improper Authentication

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Affected products

Openbsd Openssh: before 7.2
Debian Linux: 8.0
Oracle Linux: 6; 7
Red Hat Enterprise Linux Desktop: 6.0; 7.0
Red Hat Enterprise Linux Eus: 7.2; 7.3; 7.4; 7.5; 7.6; 7.7
Red Hat Enterprise Linux Server: 6.0; 7.0
Red Hat Enterprise Linux Server Aus: 7.2; 7.3; 7.4; 7.6; 7.7
Red Hat Enterprise Linux Server Tus: 7.2; 7.3; 7.6; 7.7
Red Hat Enterprise Linux Workstation: 6.0; 7.0