A certain Debian patch for OpenSSH before 4.3p2-9etch3 on etch; before 4.6p1-1 on sid and lenny; and on other distributions such as SUSE uses functions that are not async-signal-safe in the signal handler for login timeouts, which allows remote attackers to cause a denial of service (connection slot exhaustion) via multiple login attempts. NOTE: this issue exists because of an incorrect fix for CVE-2006-5051.

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.

Due to a faulty signal handler repeated login attempts could exhaust the maximum allowed connections and prevent further logins.
(CVE-2008-4109)

It was discovered that the ForceCommand directive could be bypassed.
If a local user created a malicious ~/.ssh/rc file, they could execute arbitrary commands as their user id. This only affected Ubuntu 7.10.
(CVE-2008-1657)

USN-355-1 fixed vulnerabilities in OpenSSH. It was discovered that the fixes for this issue were incomplete. A remote attacker could attempt multiple logins, filling all available connection slots, leading to a denial of service. This only affected Ubuntu 6.06 and 7.04.
(CVE-2008-4109).

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.

Due to a faulty signal handler repeated login attempts could exhaust the maximum allowed connections and prevent further logins.
(CVE-2008-4109)

A problem where utmp entries where not deleted when users logged out was also fixed.

It has been discovered that the signal handler implementing the login timeout in Debian's version of the OpenSSH server uses functions which are not async-signal-safe, leading to a denial of service vulnerability (CVE-2008-4109 ).

The problem was originally corrected in OpenSSH 4.4p1 (CVE-2006-5051 ), but the patch backported to the version released with etch was incorrect.

Systems affected by this issue suffer from lots of zombie sshd processes. Processes stuck with a '[net]' process title have also been observed. Over time, a sufficient number of processes may accumulate such that further login attempts are impossible. Presence of these processes does not indicate active exploitation of this vulnerability.
It is possible to trigger this denial of service condition by accident.

Tavis Ormandy discovered that the SSH daemon did not properly handle authentication packets with duplicated blocks. By sending specially crafted packets, a remote attacker could exploit this to cause the ssh daemon to drain all available CPU resources until the login grace time expired. (CVE-2006-4924)

Mark Dowd discovered a race condition in the server's signal handling.
A remote attacker could exploit this to crash the server.
(CVE-2006-5051).

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.

Tavis Ormandy of the Google Security Team discovered a Denial of Service vulnerability in the SSH protocol version 1 CRC compensation attack detector. This could allow a remote unauthenticated attacker to trigger excessive CPU utilization by sending a specially crafted SSH message, which would then deny ssh services to other users or processes (CVE-2006-4924, CVE-2006-4925). Please note that Mandriva ships with only SSH protocol version 2 enabled by default.

Next, an unsafe signal handler was found by Mark Dowd. This signal handler was vulnerable to a race condition that could be exploited to perform a pre-authentication DoS, and theoretically a pre-authentication remote code execution in the case where some authentication methods like GSSAPI are enabled (CVE-2006-5051).

Updated packages have been patched to correct this issue.

The version of OpenSSH running on the remote host is prior to version 4.4. Such versions are affected by multiple vulnerabilities:

 - A race condition exists that may allow an unauthenticated, remote attacker to crash the service or, on portable OpenSSH, possibly execute code on the affected host. Note that successful exploitation requires that GSSAPI authentication be enabled.
 - A flaw exists that may allow an attacker to determine the validity of usernames on some platforms. Note that this issue requires that GSSAPI authentication be enabled.
 - When SSH version 1 is used, an issue can be triggered via an SSH packet that contains duplicate blocks that could result in a loss of availability for the service.
 - On Fedora Core 6 (and possibly other systems), an unspecified vulnerability in the linux_audit_record_event() function allows remote attackers to inject incorrect information into audit logs.

According to its banner, the version of OpenSSH installed on the remote host is affected by multiple vulnerabilities :

  - A race condition exists that may allow an     unauthenticated, remote attacker to crash the service     or, on portable OpenSSH, possibly execute code on the     affected host.  Note that successful exploitation     requires that GSSAPI authentication be enabled.
    
  - A flaw exists that may allow an attacker to determine     the validity of usernames on some platforms. Note that     this issue requires that GSSAPI authentication be     enabled.

  - When SSH version 1 is used, an issue can be triggered     via an SSH packet that contains duplicate blocks that     could result in a loss of availability for the service.

  - On Fedora Core 6 (and possibly other systems), an     unspecified vulnerability in the     linux_audit_record_event() function allows remote     attackers to inject incorrect information into     audit logs.

ID	Name	Product	Family	Severity
55992	SunSSH < 1.1.1 / 1.3 CBC Plaintext Disclosure	Nessus	Misc.	critical
41244	SuSE9 Security Update : OpenSSH (YOU Patch Number 12257)	Nessus	SuSE Local Security Checks	medium
36855	Ubuntu 6.06 LTS / 7.04 / 7.10 : openssh vulnerabilities (USN-649-1)	Nessus	Ubuntu Local Security Checks	high
34321	SuSE 10 Security Update : OpenSSH (ZYPP Patch Number 5627)	Nessus	SuSE Local Security Checks	medium
34223	Debian DSA-1638-1 : openssh - denial of service	Nessus	Debian Local Security Checks	high
27935	Ubuntu 5.04 / 5.10 / 6.06 LTS : openssh vulnerabilities (USN-355-1)	Nessus	Ubuntu Local Security Checks	high
24565	Mandrake Linux Security Advisory : openssh (MDKSA-2006:179)	Nessus	Mandriva Local Security Checks	high
3751	OpenSSH < 4.4 Multiple Vulnerabilities	Nessus Network Monitor	SSH	low
22466	OpenSSH < 4.4 Multiple Vulnerabilities	Nessus	Misc.	high

Detections

Analytics

CVE-2008-4109

high

Tenable Plugins

critical

medium

high

medium

high

high

high

low

high