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Vulnerability · Published May 29, 2026 · Assigned by GitHub_M

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

Medium 5.3

In plain English

A medium-severity improper input validation in cpp-httplib from yhirose. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities).

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.3%top 74.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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 (§7.22.1.4), strtoul silently accepts a leading minus sign, performing unsigned wrap-around: strtoul("-2", …, 16) returns ULONG_MAX − 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12cpp-httplibno fix listedDEBIAN-CVE-2026-45352
Debian:13cpp-httplibno fix listedDEBIAN-CVE-2026-45352
Debian:14cpp-httplibno fix listedDEBIAN-CVE-2026-45352
Ubuntu:25.10cpp-httplibno fix listedUBUNTU-CVE-2026-45352
Ubuntu:26.10cpp-httplibno fix listedUBUNTU-CVE-2026-45352

Affected products (as reported)

VendorProductVersions
yhirose cpp-httplib < 0.43.4

Weakness: CWE-20, CWE-1285, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References