OpenSSH < 9.8 RCE

high Nessus Plugin ID 201194

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Synopsis

The SSH server running on the remote host is affected by a vulnerability.

Description

The version of OpenSSH installed on the remote host is prior to 9.8. It is, therefore, affected by a vulnerability as referenced in the release-9.8 advisory.

- This release contains fixes for two security problems, one critical and one minor. 1) Race condition in sshd(8) A critical vulnerability in sshd(8) was present in Portable OpenSSH versions between 8.5p1 and 9.7p1 (inclusive) that may allow arbitrary code execution with root privileges. Successful exploitation has been demonstrated on 32-bit Linux/glibc systems with ASLR. Under lab conditions, the attack requires on average 6-8 hours of continuous connections up to the maximum the server will accept. Exploitation on 64-bit systems is believed to be possible but has not been demonstrated at this time. It's likely that these attacks will be improved upon. Exploitation on non-glibc systems is conceivable but has not been examined. Systems that lack ASLR or users of downstream Linux distributions that have modified OpenSSH to disable per-connection ASLR re-randomisation (yes - this is a thing, no - we don't understand why) may potentially have an easier path to exploitation. OpenBSD is not vulnerable. We thank the Qualys Security Advisory Team for discovering, reporting and demonstrating exploitability of this problem, and for providing detailed feedback on additional mitigation measures. 2) Logic error in ssh(1) ObscureKeystrokeTiming In OpenSSH version 9.5 through 9.7 (inclusive), when connected to an OpenSSH server version 9.5 or later, a logic error in the ssh(1) ObscureKeystrokeTiming feature (on by default) rendered this feature ineffective - a passive observer could still detect which network packets contained real keystrokes when the countermeasure was active because both fake and real keystroke packets were being sent unconditionally. This bug was Daniel Hugenroth and Alastair Beresford of the University of Cambridge Computer Lab. Worse, the unconditional sending of both fake and real keystroke packets broke another long- standing timing attack mitigation. Since OpenSSH 2.9.9 sshd(8) has sent fake keystoke echo packets for traffic received on TTYs in echo-off mode, such as when entering a password into su(8) or sudo(8). This bug rendered these fake keystroke echoes ineffective and could allow a passive observer of a SSH session to once again detect when echo was off and obtain fairly limited timing information about keystrokes in this situation (20ms granularity by default). This additional implication of the bug was identified by Jacky Wei En Kung, Daniel Hugenroth and Alastair Beresford and we thank them for their detailed analysis.
This bug does not affect connections when ObscureKeystrokeTiming was disabled or sessions where no TTY was requested. (openssh-9.8-1)

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

Solution

Upgrade to OpenSSH version 9.8 or later.

Plugin Details

Severity: High

ID: 201194

File Name: openssh_98.nasl

Version: 1.4

Type: remote

Family: Misc.

Published: 7/1/2024

Updated: 7/11/2024

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 5.9

CVSS v2

Risk Factor: High

Base Score: 7.6

Temporal Score: 6

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

CVSS Score Source: CVE-2024-6387

CVSS v3

Risk Factor: High

Base Score: 8.1

Temporal Score: 7.3

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:P/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:openbsd:openssh

Required KB Items: installed_sw/OpenSSH

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 7/1/2024

Vulnerability Publication Date: 7/1/2024

Reference Information

CVE: CVE-2024-39894, CVE-2024-6387

IAVA: 2024-A-0375

Detections

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