PIZZACODE SECURITY ALERT program: rssh risk: low[*] problem: string format vulnerability in log.c details: rssh is a restricted shell for use with OpenSSH, allowing only scp and/or sftp. For example, if you have a server which you only want to allow users to copy files off of via scp, without providing shell access, you can use rssh to do that. Additioanlly, running rsync, rdist, and cvs are supported, and access can be configured on a per-user basis using a simple text-based configuration file. The rssh homepage is here: http://www.pizzashack.org/rssh/ Florian Schilhabel has identified a format string bug which can allow an attacker to run arbitrary code from an account configured to use rssh. [*]In general the risk is low, as in most cases the user can only compromise their own account. The risk is mittigated by the fact that before this bug can be exploited, the user must log in successfully through ssh. This means that either the user is known to the system (and therefore the administrators), or that the system is probably already compromised. However, on some older systems with broken implementations of the setuid() family of functions, a root compromise may be possible with certain configurations of rssh. Specifically, if rssh is configured to use a chroot jail, it will exec() rssh_chroot_helper, which must be setuid root in order to call chroot(). Normally, rssh_chroot_helper calls setuid(getuid()) and drops privileges before any of the logging functions are called, making a root compromise impossible on most systems. However, some older systems which handle saved UIDs improperly may be vulnerable to a root compromise. Linux in particular is not vulnerable to this, nor should modern POSIX-compliant Unix variants be. POSIX defines that the setuid() system call will set all UIDs (UID, saved UID, and effective UID) the specified UID if it is called with root privileges. Therefore in general, a root compromise is not possible, and I am not specifically aware of any systems on which one is possible. The 2.2.2 release of rssh fixes this string format vulnerability. I have also gone over the code to make sure that no other such vulnerabilities exist. In addition to fixing this problem, rssh contains some new code to help identify certain problems for debugging problems when rssh fails. Additional logging of error conditions is performed. -- Derek D. Martin http://www.pizzashack.org/ GPG Key ID: 0x81CFE75D
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