A publicly available exploit tool that exploits a vulnerability in Apache HTTP Server could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected system. Apache has reported that active use of this tool has been observed.
The vulnerability, documented in Alert 24004, exists because the affected software incorrectly processes a Range Retrieval Request header that is received via an HTTP request. Due to the flaw, upon receiving a request with a 0-byte range or overlapping byte ranges, the affected software erroneously allocates a bucket for each byte requested and stores them in a brigade.
The tool allows an unauthenticated, remote attacker to send malicious HTTP requests to the affected system, triggering excessive memory consumption that could lead to a DoS condition.
Administrators are advised to contact the vendor regarding future updates and releases. Until updates can be applied, administrators are advised to configure connection throttling or filtering of repetitive, abusive connection requests.
Apache has confirmed the vulnerability in a security announcement. Updated software is not available; however, Apache has released approved workarounds.
Apache has released a security announcement at the following link: CVE-2011-3192