FreeBSD Security Advisory (FreeBSD-SA-03:15.openssh.asc)

Published: 2008-09-04 18:41:11

CVSS Base Vector:
AV:N/AC:L/Au:N/C:C/I:C/A:C

Technical Details:
OpenSSH is a free version of the SSH protocol suite of network connectivity tools. OpenSSH encrypts all traffic (including passwords) to effectively eliminate eavesdropping, connection hijacking, and other network-level attacks. Additionally, OpenSSH provides a myriad of secure tunneling capabilities, as well as a variety of authentication methods. The SSH protocol exists in two versions, hereafter named simply `ssh1' and `ssh2'. The ssh1 protocol is a legacy protocol for which there exists no formal specification, while the ssh2 protocol is the product of the IETF SECSH working group and is defined by a series of IETF draft standards. The ssh2 protocol supports a wide range of authentication mechanisms, including a generic challenge / response mechanism, called `keyboard-interactive' or `kbdint', which can be adapted to serve any authentication scheme in which the server and client exchange a arbitrarily long series of challenges and responses. In particular, this mechanism is used in OpenSSH to support PAM authentication. The ssh1 protocol, on the other hand, supports a much narrower range of authentication mechanisms. Its challenge / response mechanisms, called `TIS', allows for only one challenge from the server and one response from the client. OpenSSH contains interface code which allows kbdint authentication back-ends to be used for ssh1 TIS authentication, provided they only emit one challenge and expect only one response. Finally, recent versions of OpenSSH implement a mechanism called `privilege separation' in which the task of communicating with the client is delegated to an unprivileged child process, while the privileged parent process performs the actual authentication and double-checks every important decision taken by its unprivileged child. 1) Insufficient checking in the ssh1 challenge / response interface code, combined with a peculiarity of the PAM kbdint back-end, causes OpenSSH to ignore a negative result from PAM (but not from any other kbdint back-end). 2) A variable used by the PAM conversation function to store challenges and the associated client responses is incorrectly interpreted as an array of pointers to structures instead of a pointer to an array of structures. 3) When challenge / response authentication is used with protocol version 1, and a legitimate user interrupts challenge / response authentication but successfully authenticates through some other mechanism (such as password authentication), the server fails to reclaim resources allocated by the challenge / response mechanism, including the child process used for PAM authentication. When a certain number of leaked processes is reached, the master server process will refuse subsequent client connections.

Recommendations:
Upgrade your system to the appropriate stable release or security branch dated after the correction date https://secure1.securityspace.com/smysecure/catid.html?in=FreeBSD-SA-03:15.openssh.asc

Summary:
The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-03:15.openssh.asc

Detection Type:
Linux Distribution Package

Solution Type:
Vendor Patch

Severity
High
CVSS Score
10.0
Published
2008-09-04
Modified
2017-12-07
Category
FreeBSD Local Security Checks

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