Overview
This report will detail an important vulnerability in cpp-httplib, a C++ HTTP/HTTPS server and client library widely used in applications. The flaw, designated as CVE-2025-46728, can lead to system memory exhaustion and potentially cause a server crash or unresponsiveness. This makes it a serious concern for organizations relying on apps built with cpp-httplib, potentially exposing them to data leakage or system compromise.
Vulnerability Summary
CVE ID: CVE-2025-46728
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Uncontrolled memory allocation leading to system memory exhaustion, server crash or unresponsiveness, and potential data leakage or system compromise.
Affected Products
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Product | Affected Versions
cpp-httplib | Prior to 0.20.1
How the Exploit Works
The vulnerability arises when the cpp-httplib library processes incoming request bodies with `Transfer-Encoding: chunked` or when no `Content-Length` header is provided. A remote attacker can exploit this by sending a chunked request without the terminating zero-length chunk, leading to uncontrolled memory allocation on the server. This could potentially exhaust system memory, causing server crash or unresponsiveness.
Conceptual Example Code
The following HTTP request is a
conceptual
example of how the vulnerability might be exploited.
POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Transfer-Encoding: chunked
{ "malicious_payload": "..." }Impact Summary
A successful exploit could lead to potential system compromise or data leakage. This includes the possibility of uncontrolled memory allocation, system memory exhaustion, server crash or unresponsiveness.
Mitigation Guidance
Organizations are advised to apply the vendor patch by updating to cpp-httplib version 0.20.1 or later. If updating immediately is not feasible, a short-term workaround is available. Deploy a reverse proxy (e.g., Nginx, HAProxy) in front of the cpp-httplib application and configure it to enforce maximum request body size limits. This would stop excessively large requests before they reach the vulnerable library code. As a temporary mitigation, using a WAF/IDS is also recommended.
