Description

The RTSP handler in libalias rewrote outgoing packets into a fixed-length stack buffer without checking whether the rewritten data fit in the buffer, or whether the result fit back in the original packet. A host sending crafted RTSP traffic from inside a NAT gateway using libalias can overflow a stack buffer, potentially achieving remote code execution in the kernel (when using ipfw(4) NAT) or in the natd(8) process (which generally runs as the root user).

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-19T06:17:40.790Z",
  "pubdate": "2026-08-19T06:17:40.790Z",
  "executiveSummary": "A stack-based buffer overflow vulnerability exists within the RTSP handler of libalias. The flaw arises due to the lack of boundary checks when rewriting outgoing packets into a fixed-length stack buffer and when evaluating whether the resulting payload fits back into the original packet structure.\nThe impact of this vulnerability is severe, potentially allowing an attacker to achieve remote code execution. Because libalias is utilized by network address translation mechanisms, successful exploitation can compromise the kernel when operating via ipfw(4) NAT, or compromise the natd(8) process, which typically executes with root privileges.\nAffected systems include environments utilizing libalias for RTSP NAT processing, specifically deployments leveraging ipfw(4) NAT or natd(8). The risk implications are critical, as they encompass full system or kernel compromise.\nThe threat actor capability required involves the ability to send crafted RTSP traffic from inside a NAT gateway utilizing libalias. No specific authentication requirements or advanced exploitation prerequisites beyond crafting and transmitting malicious RTSP streams are detailed in the input.",
  "technicalDetails": "The root cause of the vulnerability is an insufficient bounds-checking mechanism within the RTSP handler component of libalias. Specifically, when processing and rewriting outgoing RTSP packets, the implementation copies data into a fixed-length stack buffer without verifying if the incoming or rewritten data exceeds the allocated buffer capacity.\nFurthermore, the handler fails to validate whether the resulting rewritten packet size fits back within the constraints of the original packet boundaries, introducing memory corruption vectors.\nThe vulnerable component is the RTSP packet handling routine within libalias. The attack flow begins when an attacker positioned inside a NAT gateway transmits maliciously crafted RTSP traffic destined to be processed by the affected NAT facility.\nAs the libalias subsystem parses and handles the crafted RTSP traffic, it triggers the vulnerable packet rewriting logic. The unchecked string or data manipulation overflows the fixed-length stack buffer on the call stack.\nDepending on the operational context of libalias, the execution flow diverges into high-privilege domains. When libalias is integrated directly with ipfw(4) NAT, the memory corruption occurs within kernel space, potentially leading to arbitrary kernel code execution and complete operating system compromise.\nAlternatively, when libalias is utilized by the natd(8) daemon, the buffer overflow impacts the natd(8) process space. Because natd(8) generally executes with root privileges, this results in direct root-level code execution on the host system.\nPrivilege requirements for the attacker are minimal regarding authentication, but require the ability to originate or relay crafted RTSP traffic from an internal network position relative to the NAT gateway. Network exposure encompasses environments running libalias-based NAT services parsing RTSP protocol streams."
}