Bug 2446713 (CVE-2026-31870)

Summary: CVE-2026-31870 cpp-httplib: cpp-httplib: Denial of Service via malformed Content-Length header
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedCC: pemensik
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in cpp-httplib. A remote attacker, acting as a malicious server or through a man-in-the-middle position, can send a specially crafted HTTP response with a malformed Content-Length header. This lack of input validation and exception handling causes the client application to crash, resulting in a Denial of Service (DoS).
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Bug Depends On: 2446925, 2446926    
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Description OSIDB Bzimport 2026-03-11 19:01:55 UTC 
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.
Comment 2 Petr Menšík 2026-03-12 14:52:40 UTC 
Upstream security advisory: https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-39q5-hh6x-jpxx