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.

Versions of the package yhirose/cpp-httplib before 0.12.4 are vulnerable to CRLF Injection when untrusted user input is used to set the content-type header in the HTTP .Patch, .Post, .Put and .Delete requests. This can lead to logical errors and other misbehaviors. Note: This issue is present due to an incomplete fix for CVE-2020-11709.

cpp-httplib through 0.5.8 does not filter \r\n in parameters passed into the setredirect and setheader functions, which creates possibilities for CRLF injection and HTTP response splitting in some specific contexts.