Microsoft Windows is prone to a remotely exploitable heap-overflow vulnerability because the software fails to properly bounds-check user-supplied input before copying it into an insufficiently sized memory buffer. Remote attackers can exploit this issue to execute arbitrary machine code in the context of the vulnerable software on the targeted user's computer.
Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for signs of suspicious or anomalous activity. This may help detect malicious actions that an attacker may take after successfully exploiting vulnerabilities in applications. Review all applicable logs regularly.
Do not accept or execute files from untrusted or unknown sources.
Users should never accept files from untrusted or unknown sources, because they may be malicious in nature. Avoid opening email attachments from unknown or questionable sources.
Do not accept communications that originate from unknown or untrusted sources.
Do not follow links or open email from unknown or untrusted sources.
Implement multiple redundant layers of security.
Since this issue may be leveraged to execute code, we recommend memory-protection schemes, such as nonexecutable stack/heap configurations and randomly mapped memory segments. This tactic may complicate exploit attempts of memory-corruption vulnerabilities.
Run all software as a nonprivileged user with minimal access rights.
To mitigate the impact of a successful exploit, run the affected applications as a user with minimal access rights.
Disable any services that are not needed.
Since a successful exploit may require users to view HTML content in email messages, consider disabling HTML rendering in email clients to mitigate the possibility of remote exploitation. Note that disabling HTML content in email clients may reduce functionality.
The vendor has released an advisory and updates. Please see the references for details. UPDATE (08/25/09): Microsoft has re-released Japanese language updates for Windows XP Service Pack 2, Windows XP Service Pack 3, and Windows XP Professional x64 Edition Service Pack 2. Please see the MS09-029 to obtain re-released updates.