OpenSSH 9.5 through 9.7 before 9.8 sometimes allows timing attacks against echo-off password entry (e.g., for su and Sudo) because of an ObscureKeystrokeTiming logic error. Similarly, other timing attacks against keystroke entry could occur.

The remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 / openSUSE 15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2024:2393-1 advisory.

    Security fixes:

    - CVE-2024-39894: Fixed timing attacks against echo-off password entry (bsc#1227318).

    Other fixes:
    - Add obsoletes for openssh-server-config-rootlogin (bsc#1227350).
    - Add #include <stdlib.h> in some files added by the ldap patch to       fix build with gcc14 (bsc#1225904).
    - Remove the recommendation for openssh-server-config-rootlogin       from openssh-server (bsc#1224392).

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

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

The remote Ubuntu 24.04 LTS host has packages installed that are affected by a vulnerability as referenced in the USN-6887-1 advisory.

    Philippos Giavridis, Jacky Wei En Kung, Daniel Hugenroth, and Alastair Beresford discovered that the     OpenSSH ObscureKeystrokeTiming feature did not work as expected. A remote attacker could possibly use this     issue to determine timing information about keystrokes.

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

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

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.

ID	Name	Product	Family	Severity
202175	SUSE SLED15 / SLES15 / openSUSE 15 Security Update : openssh (SUSE-SU-2024:2393-1)	Nessus	SuSE Local Security Checks	medium
202082	Ubuntu 24.04 LTS : OpenSSH vulnerability (USN-6887-1)	Nessus	Ubuntu Local Security Checks	high
201194	OpenSSH < 9.8 RCE	Nessus	Misc.	high

Detections

Analytics

CVE-2024-39894

high

Tenable Plugins

medium

high

high