Vulnerability-Lookup

CVE-2026-54902 (GCVE-0-2026-54902)

Vulnerability from cvelistv5 – Published: 2026-06-30 23:40 – Updated: 2026-07-01 12:37

Title

Oj: Use-After-Free in Oj::Parser SAJ Long Key Callback

Summary

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. Prior to version 3.17.2, is vulnerable to Use-After-Free when in SAJ mode. The Oj::Parser does not protect cached object keys (≥ 35 bytes) from garbage collection, and a Ruby callback that triggers GC inside hash_end can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address 0x4242 (a canary-style pattern suggesting control over the freed memory's content). This issue has been fixed in version 3.17.2.

Severity

6.3 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-416 - Use After Free

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/ohler55/oj/security/advisories…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
ohler55	oj	Affected: < 3.17.2

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-54902

Vulnerability from fkie_nvd - Published: 2026-07-01 00:16 - Updated: 2026-07-01 15:27

Severity

6.3 (Medium) - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/ohler55/oj/security/advisories/GHSA-m578-w5vf-rfcm
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/ohler55/oj/security/advisories/GHSA-m578-w5vf-rfcm

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "oj",
          "vendor": "ohler55",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.17.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
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      "lang": "en",
      "value": "Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. Prior to version 3.17.2, is vulnerable to Use-After-Free when in SAJ mode. The Oj::Parser does not protect cached object keys (\u2265 35 bytes) from garbage collection, and a Ruby callback that triggers GC inside hash_end can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address 0x4242 (a canary-style pattern suggesting control over the freed memory\u0027s content). This issue has been fixed in version 3.17.2."
    }
  ],
  "id": "CVE-2026-54902",
  "lastModified": "2026-07-01T15:27:14.107",
  "metrics": {
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          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.3,
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          "exploitMaturity": "NOT_DEFINED",
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GHSA-M578-W5VF-RFCM

Vulnerability from github – Published: 2026-06-19 20:47 – Updated: 2026-06-19 20:47

Summary

Oj: Use-After-Free in Oj::Parser SAJ Long Key Callback

Details

Summary

Oj::Parser in SAJ mode does not protect cached object keys (≥ 35 bytes) from garbage collection. A Ruby callback that triggers GC inside hash_end can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address 0x4242 (a canary-style pattern suggesting control over the freed memory's content).

Version

Software: oj gem
Affected: all versions with ext/oj/saj2.c / ext/oj/parser.c
Latest tested: 3.17.1 (confirmed present)

Details

Short keys (≤ 34 bytes) are stored inline on the C stack and are safe. Long keys (≥ 35 bytes) are stored as heap-allocated Ruby String objects passed to rb_funcall as the key argument. Between the key being resolved and the callback completing, a GC triggered inside the callback (e.g. GC.start) can collect the key String, leaving a dangling VALUE.

Crash output:

long_key_trigger
[BUG] Segmentation fault at 0x0000000000004242
    close_object+0x260    /ext/oj/usual.c:405  (calls rb_funcall with freed key)
    parse+0x11ff          /ext/oj/parser.c:693
    parser_parse+0x145    /ext/oj/parser.c:1408

RIP: 0x7fd1b46d68b7  RDI: 0x0000000000004242  (freed key VALUE)
R12: 0x0000000000004242

The freed VALUE 0x4242 shows the attacker-controlled content of the key string was loaded as a pointer — a classic use-after-free indicator.

Reproduce

require 'oj'

class H < Oj::Saj
  def add_value(value, key)
    GC.start(full_mark: true, immediate_sweep: true) if key == 'x'
  end
  def hash_start(key); end
  def hash_end(key); end
end

p = Oj::Parser.new(:saj)
p.handler = H.new
p.parse('{"' + 'A' * 35 + '":{"x":1}}')  # long outer key, GC fires on inner key

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

JSON

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-2026-54902"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T20:47:28Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`Oj::Parser` in SAJ mode does not protect cached object keys (\u2265 35 bytes) from garbage collection. A Ruby callback that triggers GC inside `hash_end` can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address `0x4242` (a canary-style pattern suggesting control over the freed memory\u0027s content).\n\n### Version\n\n- **Software**: oj gem\n- **Affected**: all versions with `ext/oj/saj2.c` / `ext/oj/parser.c`\n- **Latest tested**: 3.17.1 (confirmed present)\n\n### Details\n\nShort keys (\u2264 34 bytes) are stored inline on the C stack and are safe. Long keys (\u2265 35 bytes) are stored as heap-allocated Ruby String objects passed to `rb_funcall` as the `key` argument. Between the key being resolved and the callback completing, a GC triggered inside the callback (e.g. `GC.start`) can collect the key String, leaving a dangling VALUE.\n\nCrash output:\n```\nlong_key_trigger\n[BUG] Segmentation fault at 0x0000000000004242\n    close_object+0x260    /ext/oj/usual.c:405  (calls rb_funcall with freed key)\n    parse+0x11ff          /ext/oj/parser.c:693\n    parser_parse+0x145    /ext/oj/parser.c:1408\n\nRIP: 0x7fd1b46d68b7  RDI: 0x0000000000004242  (freed key VALUE)\nR12: 0x0000000000004242\n```\n\nThe freed VALUE `0x4242` shows the attacker-controlled content of the key string was loaded as a pointer \u2014 a classic use-after-free indicator.\n\n### Reproduce\n\n```ruby\nrequire \u0027oj\u0027\n\nclass H \u003c Oj::Saj\n  def add_value(value, key)\n    GC.start(full_mark: true, immediate_sweep: true) if key == \u0027x\u0027\n  end\n  def hash_start(key); end\n  def hash_end(key); end\nend\n\np = Oj::Parser.new(:saj)\np.handler = H.new\np.parse(\u0027{\"\u0027 + \u0027A\u0027 * 35 + \u0027\":{\"x\":1}}\u0027)  # long outer key, GC fires on inner key\n```",
  "id": "GHSA-m578-w5vf-rfcm",
  "modified": "2026-06-19T20:47:28Z",
  "published": "2026-06-19T20:47:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ohler55/oj/security/advisories/GHSA-m578-w5vf-rfcm"
    },
    {
      "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::Parser SAJ Long Key Callback"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-54902 (GCVE-0-2026-54902)

FKIE_CVE-2026-54902

GHSA-M578-W5VF-RFCM

Summary

Version

Details

Reproduce

Tags

Sightings

Nomenclature