cpp-httplib has Unbounded Memory Allocation in Chunked/No-Length Requests

Vulnerability Description

cpp-httplib is a C++ header-only HTTP/HTTPS server and client library. Prior to version 0.20.1, the library fails to enforce configured size limits on incoming request bodies when `Transfer-Encoding: chunked` is used or when no `Content-Length` header is provided. A remote attacker can send a chunked request without the terminating zero-length chunk, causing uncontrolled memory allocation on the server. This leads to potential exhaustion of system memory and results in a server crash or unresponsiveness. Version 0.20.1 fixes the issue by enforcing limits during parsing. If the limit is exceeded at any point during reading, the connection is terminated immediately. A short-term workaround through a Reverse Proxy is available. If updating the library immediately is not feasible, deploy a reverse proxy (e.g., Nginx, HAProxy) in front of the `cpp-httplib` application. Configure the proxy to enforce maximum request body size limits, thereby stopping excessively large requests before they reach the vulnerable library code.

References

• https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-px83-72rx-v57c
• https://github.com/yhirose/cpp-httplib/commit/7b752106ac42bd5b907793950d9125a0972c8e8e