cpp-httplib DoS: Negative chunk-size in chunked Transfer-Encoding
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.
Problem Types
| Type | CWE ID | Description |
|---|
| CWE | CWE-20 | CWE-20: Improper Input Validation |
| CWE | CWE-1285 | CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input |
| CWE | CWE-770 | CWE-770: Allocation of Resources Without Limits or Throttling |
Type: CWE
Description: CWE-20: Improper Input Validation
Type: CWE
Description: CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input
Type: CWE
Description: CWE-770: Allocation of Resources Without Limits or Throttling
Metrics
| Version | Base score | Base severity | Vector |
|---|
| 3.1 | 5.3 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
Version: 3.1
Base score: 5.3
Base severity: MEDIUM
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L