GHSA-9PPP-W3G4-FH4Q

Vulnerability from github – Published: 2026-06-19 19:36 – Updated: 2026-06-19 19:36
VLAI
Summary
Oj: Use-After-Free in Oj::Doc Iterators via Reentrant Close
Details

Summary

Oj::Doc iterators (each_value, each_child, each_leaf) are vulnerable to a heap use-after-free. When a Ruby block yielded during iteration calls doc.close or d.close, the document's heap memory is freed while the C iterator is still running. When control returns from the block, the iterator reads from the freed region, producing a use-after-free accessible from pure Ruby.

Version

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

Details

The iterators in ext/oj/fast.c follow the pattern:

// fast.c:1505 (doc_each_child)
static VALUE doc_each_child(VALUE self, ...) {
    ...
    while (cur != NULL) {
        rb_yield(...);       // ← Ruby block executes here
        cur = cur->next;     // ← cur is now freed if block called close()
    }
}

rb_yield can invoke arbitrary Ruby code, including calling close() on the Doc or any child node, which calls ruby_sized_xfree on the backing buffer. On return, the C code reads cur->next from the freed region. All three iterators are affected.

ASAN report (each_child variant):

==253632==ERROR: AddressSanitizer: heap-use-after-free on address 0x5210000bd080
READ of size 8 at 0x5210000bd080 thread T0
    #0 doc_each_child  /ext/oj/fast.c:1505
0x5210000bd080 is located 896 bytes inside of 4064-byte region [0x5210000bcd00, 0x5210000bdce0)
freed by thread T0 here:
    #0 free
    #1 ruby_sized_xfree  (libruby-3.3.so.3.3)

All three iterators trigger the same freed region (fd shadow bytes):

0x5210000bd080:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd

Reproduce

require 'oj'
# each_child
Oj::Doc.open('[1,2]') { |doc| doc.each_child { |d| d.close } }
# each_value
Oj::Doc.open('[1,2]') { |doc| doc.each_value { |v| doc.close } }
# each_leaf
Oj::Doc.open('[1,[2]]') { |doc| doc.each_leaf { |d| d.close } }
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
To clipboard 

{
  "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-2026-54897"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T19:36:50Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`Oj::Doc` iterators (`each_value`, `each_child`, `each_leaf`) are vulnerable to a heap use-after-free. When a Ruby block yielded during iteration calls `doc.close` or `d.close`, the document\u0027s heap memory is freed while the C iterator is still running. When control returns from the block, the iterator reads from the freed region, producing a use-after-free accessible from pure Ruby.\n\n### Version\n\n- **Software**: oj gem\n- **Affected**: all versions with `ext/oj/fast.c`\n- **Latest tested**: 3.17.1 (confirmed present)\n\n### Details\n\nThe iterators in `ext/oj/fast.c` follow the pattern:\n\n```c\n// fast.c:1505 (doc_each_child)\nstatic VALUE doc_each_child(VALUE self, ...) {\n    ...\n    while (cur != NULL) {\n        rb_yield(...);       // \u2190 Ruby block executes here\n        cur = cur-\u003enext;     // \u2190 cur is now freed if block called close()\n    }\n}\n```\n\n`rb_yield` can invoke arbitrary Ruby code, including calling `close()` on the `Doc` or any child node, which calls `ruby_sized_xfree` on the backing buffer. On return, the C code reads `cur-\u003enext` from the freed region. All three iterators are affected.\n\nASAN report (each_child variant):\n```\n==253632==ERROR: AddressSanitizer: heap-use-after-free on address 0x5210000bd080\nREAD of size 8 at 0x5210000bd080 thread T0\n    #0 doc_each_child  /ext/oj/fast.c:1505\n0x5210000bd080 is located 896 bytes inside of 4064-byte region [0x5210000bcd00, 0x5210000bdce0)\nfreed by thread T0 here:\n    #0 free\n    #1 ruby_sized_xfree  (libruby-3.3.so.3.3)\n```\n\nAll three iterators trigger the same freed region (`fd` shadow bytes):\n```\n0x5210000bd080:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd\n```\n\n### Reproduce\n\n```ruby\nrequire \u0027oj\u0027\n# each_child\nOj::Doc.open(\u0027[1,2]\u0027) { |doc| doc.each_child { |d| d.close } }\n# each_value\nOj::Doc.open(\u0027[1,2]\u0027) { |doc| doc.each_value { |v| doc.close } }\n# each_leaf\nOj::Doc.open(\u0027[1,[2]]\u0027) { |doc| doc.each_leaf { |d| d.close } }\n```",
  "id": "GHSA-9ppp-w3g4-fh4q",
  "modified": "2026-06-19T19:36:50Z",
  "published": "2026-06-19T19:36:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ohler55/oj/security/advisories/GHSA-9ppp-w3g4-fh4q"
    },
    {
      "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: Use-After-Free in Oj::Doc Iterators via Reentrant Close"
}


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