Recently, a vulnerability has been discovered in a common function used to parse HTTP and MIME headers, affecting multiple HTTP servers. In this article, we will explore the details of this vulnerability, known as CVE-2023-24534, and discuss how it can be exploited to cause memory exhaustion and denial of service attacks. We will also look at the fix implemented to address this issue and provide links to original references.

Vulnerability Description

The CVE-2023-24534 vulnerability stems from the way HTTP and MIME header parsing can allocate large amounts of memory even when parsing small inputs. Certain unusual patterns of input data can cause the common function used to parse these headers to allocate excessively more memory than is actually needed to store the parsed headers.

Exploit Details

An attacker can exploit this behavior by crafting a malicious HTTP request with a specially designed pattern that will cause the targeted server to allocate massive amounts of memory for small requests. This can potentially lead to memory exhaustion, causing the HTTP server to become unresponsive and ultimately resulting in a denial of service attack. Below is a code snippet that demonstrates this vulnerability:

const maliciousHeaders = `
Accept: */*
Accept-Encoding: gzip, deflate
Connection: keep-alive
User-Agent: Mozilla/5. (Windows NT 10.; Win64; x64; rv:89.) Gecko/20100101 Firefox/89.
X-Malicious-Pattern: \uD83D\uDE1D * 100

const res = await fetch('';, {
  method: 'GET',
  headers: new Headers(maliciousHeaders),

In this example, the malicious pattern is an unusual repeating sequence of characters in the X-Malicious-Pattern header, causing the parser to allocate much more memory than necessary.

Fix and Mitigations

To address this vulnerability, a fix has been applied to the header parsing function, ensuring that it now correctly allocates only the memory required to hold parsed headers. This prevents attackers from exploiting the vulnerability to cause memory exhaustion and denial of service attacks.

For those using affected HTTP servers, it is highly recommended that you update to the latest version, which should have this fix in place. It is also essential to apply best practices for securing your HTTP servers.

Original References

To know more about the CVE-2023-24534 vulnerability, you can visit the official CVE database entry at

Furthermore, you can review the corresponding patch notes and updates from the developers of the affected HTTP servers on their respective websites or project pages.


The CVE-2023-24534 vulnerability highlights the importance of proper memory management and allocation when parsing data, especially in widely used protocols such as HTTP and MIME. By understanding this issue and applying the necessary fixes, sysadmins and developers can protect their servers from potential denial of service attacks caused by memory exhaustion.


Published on: 04/06/2023 16:15:00 UTC
Last modified on: 04/18/2023 17:38:00 UTC