Use-After-Free in oj (CVE-2026-54898)
Summary
Vulnerability in oj (CVE-2026-54898). Risk of unauthorized operations or information disclosure. Exploitable via hash_start. Mitigation: upgrade to 3.17.3 or later.
Original description
The description as published by the source.
Summary
Oj::Parser#parse is vulnerable to a heap use-after-free when a SAJ/SAJ2 callback mutates the input JSON string during parsing. The C engine holds a raw const byte * pointer into the Ruby string's internal buffer. If a callback (e.g. hash_start) resizes the string — for example by calling String#replace with a longer value — Ruby reallocates the string buffer and frees the old one. The C parser's pointer is left dangling; the next character read at parser.c:607 is a use-after-free.
Version
- Software: oj gem
- Affected: all versions with
ext/oj/parser.c - Latest tested: 3.17.1 (confirmed present)
Details
ext/oj/parser.c, parser_parse → parse:
static VALUE parser_parse(VALUE self, VALUE json) {
const byte *ptr = (const byte *)StringValuePtr(json); // raw pointer into Ruby string
// ...
parse(p, ptr); // ptr used throughout; any realloc frees the backing buffer
}
// parser.c:607
static void parse(ojParser p, const byte *json) {
const byte *b = json;
// ...
for (; '\0' != *b; b++) { // ← UAF: reads freed memory after callback resizes json
Ruby's String#replace (or <<, gsub!, etc.) can trigger a reallocation of the string's internal buffer if the new content is larger than the embedded capacity, freeing the old buffer that ptr still points to.
ASAN report:
==372273==ERROR: AddressSanitizer: heap-use-after-free on address 0x51900008ed81
READ of size 1 at 0x51900008e…
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-2026-54898 has been found in oj.
Attackers can target a specific entry point like hash_start 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-2026-54898" on the vendor's site.
CVE-2026-54898 (oj) — CWE-416
Attack surface: hash_start / parser_parse / parse / ptr
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_start.
Check the vendor advisory for the affected versions of oj. Attack surface: hash_start / parser_parse / parse / ptr.
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-2026-54898 ruby-oj Fixed in: 3.14.2-1+deb12u1
- Ubuntu UBUNTU-CVE-2026-54898 ruby-oj
References
- package github.com
- web github.com
- web github.com