OpenSSH-portable (OpenSSH) 3.6.1p1 and earlier with PAM support enabled immediately sends an error message when a user does not exist, which allows remote attackers to determine valid usernames via a timing attack.

The version of SunSSH running on the remote host has an information disclosure vulnerability.  A design flaw in the SSH specification could allow a man-in-the-middle attacker to recover up to 32 bits of plaintext from an SSH-protected connection in the standard configuration.  An attacker could exploit this to gain access to sensitive information.

Note that this version of SunSSH is also prone to several additional issues but Nessus did not test for them.

@Mediaservice.net discovered two information leaks in the OpenSSH server. When using password authentication, an attacker could test whether a login name exists by measuring the time between failed login attempts, i. e. the time after which the 'password:' prompt appears again.

A similar issue affects systems which do not allow root logins over ssh ('PermitRootLogin no'). By measuring the time between login attempts an attacker could check whether a given root password is correct. This allowed determining weak root passwords using a brute force attack.

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The remote host is using a version of Portable OpenSSH that may allow an attacker to determine if an account exists or not by a timing analysis. 

Updated OpenSSH packages are now available. These updates close an information leak caused by sshd's interaction with the PAM system.

OpenSSH is a suite of network connectivity tools that can be used to establish encrypted connections between systems on a network and can provide interactive login sessions and port forwarding, among other functions.

When configured to allow password-based or challenge-response authentication, sshd (the OpenSSH server) uses PAM (Pluggable Authentication Modules) to verify the user's password. Under certain conditions, OpenSSH versions prior to 3.6.1p1 reject an invalid authentication attempt without first attempting authentication using PAM.

If PAM is configured with its default failure delay, the amount of time sshd takes to reject an invalid authentication request varies widely enough that the timing variations could be used to deduce whether or not an account with a specified name existed on the server.
This information could then be used to narrow the focus of an attack against some other system component.

These updates contain backported fixes that cause sshd to always attempt PAM authentication when performing password and challenge-response authentication for clients.

The remote host seems to be running an SSH server that could allow an attacker to determine the existence of a given login by comparing the time the remote sshd daemon takes to refuse a bad password for a nonexistent login compared to the time it takes to refuse a bad password for a valid login.

An attacker could use this flaw to set up a brute-force attack against the remote host.

ID	Name	Product	Family	Severity
55992	SunSSH < 1.1.1 / 1.3 CBC Plaintext Disclosure	Nessus	Misc.	critical
20650	Ubuntu 4.10 : openssh information leakage (USN-34-1)	Nessus	Ubuntu Local Security Checks	medium
1984	Portable OpenSSH < 3.6.1p2 PAM Timing Side-Channel Weakness	Nessus Network Monitor	SSH	medium
12407	RHEL 2.1 : openssh (RHSA-2003:224)	Nessus	Red Hat Local Security Checks	high
11574	OpenSSH w/ PAM Multiple Timing Attack Weaknesses	Nessus	Misc.	critical

Detections

Analytics

CVE-2003-0190

medium

Tenable Plugins

critical

medium

medium

high

critical