Use-After-Free in json (CVE-2026-71847)
Summary
Vulnerability in json (CVE-2026-71847). Risk of unauthorized operations or information disclosure. Exploitable via state.start. Mitigation: upgrade to 2.21.2 or later.
Original description
The description as published by the source.
Summary
Ruby's JSON native C extension clears the consumed JSON::ResumableParser input buffer but leaves state.start, state.cursor, and state.end pointing into released storage.
When partial_value reconstructs an incomplete object containing duplicate keys, the duplicate-key warning path calls cursor_position, which dereferences those stale pointers. This results in a heap-use-after-free and can terminate the Ruby process.
An attacker who can supply JSON stream data to an application using JSON::ResumableParser may cause process termination when the application calls partial_value on incomplete attacker-controlled input containing duplicate object keys.
The issue was reproduced in the native C extension from the official RubyGems releases:
- JSON 2.20.0
- JSON 2.21.0
- JSON 2.21.1
The attached evidence demonstrates:
- an AddressSanitizer-confirmed heap-use-after-free;
- a native
SIGSEGVusing the official JSON 2.21.1 RubyGem; - an end-to-end loopback TCP attacker/victim reproduction;
- four differential controls;
- successful execution after applying a tested patch control.
This was originally reported privately through Ruby's HackerOne program as report #3867755. A Ruby maintainer independently confirmed reproduction of the ASan failure and requested that further coordination continue through this private advisory.
No code execution or information disclosure is claimed.
Details
The affected source is:
ext/json/ext/parser/parser…
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-2026-71847 has been found in json.
Attackers can target a specific entry point like state.start over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade json to 2.21.2 or later.
If unsure, ask your IT team or search "json CVE-2026-71847" on the vendor's site.
CVE-2026-71847 (json) — CWE-416
Attack surface: state.start / state.cursor / state.end / partial_value
Patched: 2.21.2 — 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 json. Attackers reach the vulnerable code path via state.start.
Check the vendor advisory for the affected versions of json. Attack surface: state.start / state.cursor / state.end / partial_value.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 2.21.2.
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 'json' . 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 'json' . | 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
json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 json to 2.21.2ステージング環境で 2.21.2 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
References
- web github.com
- web github.com