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CVE-2025-53629: Memory Exhaustion Vulnerability in cpp-httplib Prior to Version 0.23.0

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Overview

This report covers a critical vulnerability found in the cpp-httplib, a C++11 single-file header-only cross platform HTTP/HTTPS library. This library, widely used in various applications for its HTTP/HTTPS functionalities, is vulnerable to an attack that can lead to memory exhaustion in the server. This issue has a significant impact as it can potentially compromise the system or result in data leakage.

Vulnerability Summary

CVE ID: CVE-2025-53629
Severity: High (7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

cpp-httplib | Prior to 0.23.0

How the Exploit Works

The vulnerability lies in the way the server handles incoming requests using the Transfer-Encoding: chunked in the header. An attacker can exploit this vulnerability by sending a specially crafted HTTP/HTTPS request with chunked Transfer-Encoding. The server then allocates memory for these chunks without any limitation, leading to memory exhaustion.

Conceptual Example Code

Below is a conceptual example of how the vulnerability might be exploited using a HTTP request:

POST / HTTP/1.1
Host: target.example.com
Transfer-Encoding: chunked
Content-Length: 9999999999
{ "malicious_payload": "..." }

In this example, the attacker sends a POST request with the Transfer-Encoding header set to chunked and an arbitrary large number for the Content-Length. The server then allocates memory based on the Content-Length, leading to memory exhaustion.

Mitigation

To mitigate this vulnerability, it is recommended to apply the vendor patch by updating cpp-httplib to version 0.23.0 or later. If the patch cannot be applied immediately, a temporary mitigation would be to use Web Application Firewall (WAF) or Intrusion Detection System (IDS) to block requests with chunked Transfer-Encoding.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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