CVE-2026-31870: Yhirose Cpp-Httplib

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.37.1, when a cpp-httplib client uses the streaming API (httplib::stream::Get, httplib::stream::Post, etc.), the library calls std::stoull() directly on the Content-Length header value received from the server with no input validation and no exception handling. std::stoull throws std::invalid_argument for non-numeric strings and std::out_of_range for values exceeding ULLONG_MAX. Since nothing catches these exceptions, the C++ runtime calls std::terminate(), which kills the process with SIGABRT. Any server the client connects to — including servers reached via HTTP redirects, third-party APIs, or man-in-the-middle positions can crash the client application with a single HTTP response. No authentication is required. No interaction from the end user is required. The crash is deterministic and immediate. This vulnerability is fixed in 0.37.1.

Affected products

• Yhirose Cpp-Httplib: before 0.37.1 (fixed in 0.37.1)

Published 2026-03-11. Last modified 2026-06-17.