There are two newly discovered flaws in widely deployed software products that present serious security problems for both users and network administrators.
The more serious of the two vulnerabilities is a buffer overflow in the OpenSSH protocol that gives a user the ability to gain root privileges on a vulnerable machine.
There is also a buffer overflow in the shell in several versions of Windows that could enable an attacker to execute code.
The OpenSSH vulnerability, revealed Thursday, is in the channel code in versions 2.0-3.0.2, and security experts say a server controlled by a malicious attacker could also exploit a connecting vulnerable client.
OpenSSH is an open-source implementation of the secure shell protocol, which enables remote users to log in securely to servers. It is used most often for secure administration of remote servers and is typically run on Unix and Linux-based systems.
The software is now maintained by the OpenBSD team, which has released an updated version of OpenSSH that corrects the problem. Many of the prominent Linux and Unix vendors also have released patches.
Buffer overflows are perhaps the most common of security vulnerabilities, but security experts say the fact that this flaw grants root privileges to users makes it far more dangerous than most.
"This gives privileged access to memory and the ability execute code at the root level, so yes its about as bad as they come," said Daniel Frasnelli, managing consultant in the vulnerability assessment division at Network Security Technologies Inc., known as Netsec, a security services company in Herndon, Va.
Frasnelli added that Netsec has received some unconfirmed reports that it is possible to exploit this flaw remotely as well.
The Windows vulnerability affects 98, NT 4.0 and 2000, but is only exploitable locally, except in rare circumstances. The buffer overflow is in a function that helps find applications that have not been uninstalled correctly. An attacker exploiting the flaw could either crash the Windows Shell or execute code with the privilege level of the local user, according to a Microsoft Corp. bulletin issued late Thursday.
If the user had installed an application with custom URL handlers, then uninstalled it incompletely, an attacker may be able to exploit the flaw remotely by constructing a Web page or sending an e-mail that contains the attack code.
Microsoft has issued a patch, which is available on the companys security Web site.