In this post, we will delve into CVE-2025-32464, a critical heap-based buffer overflow vulnerability affecting HAProxy versions 2.2 through 3.1.6 in specific, uncommon configurations. We will discuss the root cause of this vulnerability, show a code snippet illustrating the issue, provide links to original references, and outline the details of exploiting the vulnerability.

Background

HAProxy, or the High Availability Proxy, is a popular, open-source software load balancer and proxy server for TCP and HTTP-based applications. It is widely used by high-traffic websites and other organizations to distribute incoming traffic across multiple servers effectively.

Vulnerability Description

The CVE-2025-32464 vulnerability occurs due to improper handling of the replacement of multiple short patterns with a longer one in the sample_conv_regsub function. In certain uncommon configurations, this can lead to a heap-based buffer overflow, which could cause a denial of service, overwrite crucial data structures in memory, or potentially execute arbitrary code.

The vulnerable code snippet from the sample_conv_regsub function is as follows

for (i = dst + mlen; i < dmd; i--)
  buf[i - mlen] = buf[i];
return dmd - mlen;

This code is responsible for moving the memory after the matched pattern in the destination buffer. The loop iterates while i is less than dmd, decrementing i in each iteration. In specific cases, this results in a write out-of-bounds, causing a heap-based buffer overflow.

For more information on this vulnerability, the original references can be found here

1. HAProxy Security Advisory
2. CVE-2025-32464 - NVD

Exploit Details

To successfully exploit this vulnerability, an attacker must create a special HTTP request that triggers the vulnerable code path, with multiple short patterns to be replaced by a longer pattern. The exact nature of the uncommon configuration required for this attack is not disclosed to prevent abuse. However, HAProxy users are encouraged to review their configuration files and update HAProxy to a patched version.

Upon successful exploitation, range of potential impacts could occur depending on the attacker's goals, the server's configuration, and other factors. Some potential impacts include:

1. Denial of Service (DoS): Crashing the HAProxy server, causing downtime for the affected websites and services.
2. Memory Overwrite: Overwriting critical data structures in memory, leading to unintended behavior or further vulnerabilities.
3. Arbitrary Code Execution: Depending on the server's configuration and the attacker's skill level, it may be possible for the attacker to execute arbitrary code on the server, potentially gaining unauthorized access or control.

Mitigation

To mitigate this vulnerability, users of HAProxy versions 2.2 through 3.1.6 should upgrade to the latest, patched version available on the HAProxy website. Additionally, reviewing and updating HAProxy configurations to replace or eliminate the uncommon configuration could reduce the risk associated with this vulnerability.

Conclusion

In this post, we examined the details of CVE-2025-32464, a heap-based buffer overflow vulnerability affecting specific configurations of HAProxy versions 2.2 through 3.1.6. We provided a code snippet illustrating the issue, links to original references, and an outline of the exploitation process. By better understanding this vulnerability, its impact, and the proper mitigation techniques, administrators and developers can take the necessary steps to ensure their systems remain secure.

Timeline

Published on: 04/09/2025 03:15:16 UTC
Last modified on: 04/23/2025 22:15:15 UTC