Use-After-Free in oj (CVE-2026-54901)
Summary
Vulnerability in oj (CVE-2026-54901). Risk of unauthorized operations or information disclosure. Exploitable via array_class. Mitigation: upgrade to 3.17.3 or later.
Original description
The description as published by the source.
Summary
Oj::Parser in usual mode does not mark array_class and hash_class references during garbage collection. If GC runs after the class is assigned but before a parse, the class object is reclaimed, leaving the parser holding a dangling VALUE. The subsequent parse call dereferences the freed object, producing a segfault.
Version
- Software: oj gem
- Affected: all versions with
ext/oj/usual.c/ext/oj/parser.c - Latest tested: 3.17.1 (confirmed present)
Details
The parser_mark function in ext/oj/parser.c is registered as the GC mark callback for the parser's TypedData. If array_class (stored as d->array_class in the Usual struct) is not passed to rb_gc_mark, the GC does not know it is referenced and may collect it.
When close_array_class (usual.c:405) later calls rb_funcallv on the collected class VALUE, it accesses freed memory, crashing at RIP: 0x7f... / 0x0000000000000000.
Crash output:
array_class finalized
about to parse
[BUG] Segmentation fault at 0x0000000000000000
close_array_class+0x194 /ext/oj/usual.c:405
parse+0x17b3 /ext/oj/parser.c:715
parser_parse+0x10b /ext/oj/parser.c:1408
RIP: 0x7fd1b46d68b7 RBP: 0x0000000000000000
Reproduce
require 'oj'
p = Oj::Parser.new(:usual,
array_class: (ac = Class.new { def <<(_x); end }))
ObjectSpace.define_finalizer(ac, proc { warn 'array_class finalized' })
ac = nil
GC.start(full_mark: true, immediate_sweep: tr…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-54901 has been found in oj.
Attackers can target a specific entry point like array_class over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade oj to 3.17.3 or later.
If unsure, ask your IT team or search "oj CVE-2026-54901" on the vendor's site.
CVE-2026-54901 (oj) — CWE-416
Attack surface: array_class / hash_class / parse / parser_mark
Patched: 3.17.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Use-after-free (CWE-416) exists in oj. Attackers reach the vulnerable code path via array_class.
Check the vendor advisory for the affected versions of oj. Attack surface: array_class / hash_class / parse / parser_mark.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 3.17.3.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'oj' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'oj' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
ojを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade oj to 3.17.3ステージング環境で 3.17.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-54901 ruby-oj Fixed in: 3.14.2-1+deb12u1
- Ubuntu UBUNTU-CVE-2026-54901 ruby-oj
References
- package github.com
- web github.com
- web github.com