PuTTY: Pre-authentication buffer overflow

Background

PuTTY is a free implementation of Telnet and SSH for Win32 and Unix platforms, along with an xterm terminal emulator.

Description

PuTTY fails to do proper bounds checking on SSH2_MSG_DEBUG packets. The “stringlen” parameter value is incorrectly checked due to signedness issues. Note that this vulnerability is similar to the one described in GLSA 200408-04 but not the same.

Impact

When PuTTY connects to a server using the SSH2 protocol, an attacker may be able to send specially crafted packets to the client, resulting in the execution of arbitrary code with the permissions of the user running PuTTY. Note that this is possible during the authentication process but before host key verification.

Workaround

There is no known workaround at this time.

Resolution

All PuTTY users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=net-misc/putty-0.56"