Use-After-Free in oj (CVE-2026-54900)
Summary
Vulnerability in oj (CVE-2026-54900). Risk of unauthorized operations or information disclosure. Exploitable via create_id. Mitigation: upgrade to 3.17.3 or later.
Original description
The description as published by the source.
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…
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-2026-54900 has been found in oj.
Attackers can target a specific entry point like create_id 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-2026-54900" on the vendor's site.
CVE-2026-54900 (oj) — CWE-416
Attack surface: create_id / memcpy / form_attr / SIZE_MAX
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 create_id.
Check the vendor advisory for the affected versions of oj. Attack surface: create_id / memcpy / form_attr / SIZE_MAX.
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-2026-54900 ruby-oj Fixed in: 3.14.2-1+deb12u1
- Ubuntu UBUNTU-CVE-2026-54900 ruby-oj
References
- package github.com
- web github.com
- web github.com