Use-After-Free in oj (CVE-2026-54902)
Summary
Vulnerability in oj (CVE-2026-54902). Risk of unauthorized operations or information disclosure. Exploitable via hash_end. Mitigation: upgrade to 3.17.3 or later.
Original description
The description as published by the source.
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
requir…
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-2026-54902 has been found in oj.
Attackers can target a specific entry point like hash_end 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-2026-54902" on the vendor's site.
CVE-2026-54902 (oj) — CWE-416
Attack surface: hash_end / rb_funcall / key / GC.start
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 hash_end.
Check the vendor advisory for the affected versions of oj. Attack surface: hash_end / rb_funcall / key / GC.start.
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-2026-54902 ruby-oj Fixed in: 3.14.2-1+deb12u1
- Ubuntu UBUNTU-CVE-2026-54902 ruby-oj
References
- package github.com
- web github.com
- web github.com