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.

