cpp-httplib DoS: Negative chunk-size in chunked Transfer-Encoding_CVE-2026-45352

{
    "lastseen": "",
    "description": "cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.43.4, negative chunk-size in chunked Transfer-Encoding causes unbounded memory allocation and process crash. The ChunkedDecoder::read_payload function in cpp-httplib (httplib.h) parses the chunk-size field of HTTP chunked transfer encoding using std::strtoul(). Per the C standard (\u00a77.22.1.4), strtoul silently accepts a leading minus sign, performing unsigned wrap-around: strtoul(\"-2\", \u2026, 16) returns ULONG_MAX \u2212 1 (0xFFFFFFFFFFFFFFFE). The library's only guard (line 12833) rejects ULONG_MAX (the result of \"-1\"), but any other negative value such as \"-2\" passes validation. The resulting near-maximum value is stored in chunk_remaining and controls how many bytes the server's read loop consumes from the network. This vulnerability is fixed in 0.43.4.",
    "published": "2026-05-29T19:14:08.065Z",
    "modified": "2026-05-29T19:15:42.208Z",
    "type": "cve",
    "title": "cpp-httplib DoS: Negative chunk-size in chunked Transfer-Encoding",
    "source": "GitHub_M",
    "references": "https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-h6wq-j5mv-f3q8",
    "id": "CVE-2026-45352",
    "bulletinFamily": "",
    "cwe": [
        "CWE-20",
        "CWE-1285",
        "CWE-770"
    ],
    "cvelist": null,
    "sourceData": "yhirose cpp-httplib < 0.43.4",
    "sourceHref": "",
    "cvss": {
        "score": 5.3,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
        "version": "3.1"
    },
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    "href": "",
    "category_name": "CVE",
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    "product": "cpp-httplib",
    "version": "< 0.43.4",
    "vendor": "yhirose",
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    "ai_score": 0
}