The security researchers have recently discovered a critical out-of-bounds read vulnerability (CVE-2023-31122) in the mod_macro module of the Apache HTTP Server. This issue has a significant impact on the security and stability of an Apache-based web infrastructure. In this article, we'll cover the technical aspects of the vulnerability, a code snippet exhibiting the vulnerability, links to the original references, and details on how to exploit it.

Vulnerability Details

The CVE-2023-31122 vulnerability affects the mod_macro module, which is responsible for handling macros in the Apache HTTP Server. The issue lies in the module’s handling of input data, which leads to a situation where the server reads memory areas that it's not supposed to access. This out-of-bounds read can lead to information disclosure, service crashes, and potentially, the execution of arbitrary code.

The vulnerability occurred due to an error in the config.line handling during the processing of macro definitions. The vulnerability is present in versions of Apache HTTP Server through 2.4.57.

Below is a partial view of the vulnerable code found in the *mod_macro.c* file

char *current_char = config.line;
while ((arg = getword_conf(pool, &current_char)) != NULL) {

This code snippet demonstrates how the config.line handling can result in an out-of-bounds read vulnerability. The loop iterates through the config.line input until it reaches its end, but it doesn't properly check for the bounds.

Original References

The information about this vulnerability (CVE-2023-31122) is available in the following official sources:

1. CVE Information from MITRE
2. Apache’s Official Homepage

Exploit Details

At this point in time, the researchers have not released a working exploit for the CVE-2023-31122 vulnerability. However, due to the nature of the issue, any attacker with knowledge of the vulnerable module could potentially exploit the vulnerability by crafting a malicious request with specially designed macro definitions, which could trigger the out-of-bounds read.

Mitigations and Recommendations

The best way to mitigate the risks posed by the CVE-2023-31122 vulnerability is to update the Apache HTTP Server to the latest version (2.4.58 or later), as it contains patches for this issue. Additionally, the following recommendations can reduce the risk of exploitation:

Use a web application firewall (WAF) to filter out malicious traffic and requests

2. Regularly audit all installed modules and disable unnecessary ones to minimize the attack surface of the server


CVE-2023-31122 is a critical out-of-bounds read vulnerability in the mod_macro module of Apache HTTP Server. It affects versions up to 2.4.57, and exploiting it can lead to information disclosure and service crashes. It is essential to apply the necessary security patches and updates promptly to protect your web infrastructure from potential risks associated with this vulnerability. Stay vigilant, and make security a priority.


Published on: 10/23/2023 07:15:00 UTC
Last modified on: 10/30/2023 17:54:00 UTC