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CVE-2025-66570 is a critical vulnerability in cpp-httplib (up to and including version 0.26.0), a C++11 single-file header-only HTTP/HTTPS library. The vulnerability arises from improper handling of attacker-controlled HTTP headers, specifically REMOTE_ADDR, REMOTE_PORT, LOCAL_ADDR, and LOCAL_PORT. These headers, when supplied by a client, are parsed into the request header multimap before the server appends its own internal metadata using the same header names. Since Request::get_header_value returns the first value for a header key, attacker-supplied values can override server-injected metadata. This affects downstream code that relies on these headers for logging, authorization, or trust decisions, leading to potential IP spoofing, log poisoning, and authorization bypass. The vulnerable code is primarily in httplib.h (read_headers, Server::process_request, Request::get_header_value, get_header_value_u64) and affects logging and client IP extraction routines.
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A critical vulnerability in cpp-httplib related to untrusted HTTP header handling, specifically internal header shadowing, which can be exploited remotely or locally.
A critical vulnerability in cpp-httplib (≤ 0.26.0) allows attackers to override internal connection metadata (such as REMOTE_ADDR and LOCAL_ADDR) by supplying headers with reserved names, potentially misleading application logic that relies on these fields for authorization, logging, or trust decisions.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
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