JWTPatterns

Adversarial JWT library test harness: 8 libraries, 4 ecosystems, RFC 7515 compliance.

Nine attack variants. 72 test results. Six of eight libraries ship parsers that silently accept tokens with unprocessed critical extensions — a MUST-level RFC 7515 requirement that has been in the spec since 2015.

The field report

The companion article, Six of Eight JWT Libraries Ship Non-Compliant Parsers, is the writeup. This repo is the artifact. Every claim in the article traces to a committed test file and a row in results/matrix.json.

What is in here

The corpus is static and committed: one JSON file per attack variant in fixtures/corpus/, built by fixtures/generate.js from the committed test-only keypairs in fixtures/keys/ (RSA-2048 and EC P-256). Every library sees the same tokens, so the comparison is clean.

Each harness is self-contained with its own dependency manifest. Harnesses run the corpus in default configuration — no extra options, no hardening, exactly what you get when you call the library's verify function with a key and a token.

The attack variants

#	Variant	What it tests
1	RS256 to HS256 algorithm confusion	forged token signed with the server's RSA public key as an HMAC secret
2	alg:none	unsigned token with no signature
3	alg case normalization	NONE, nOnE, None, \nnone — does the parser normalize before checking?
4	jwk header injection	embedded attacker-controlled public key
5	jku header injection	URL pointing to an attacker-controlled JWK set
6	Empty signature	valid header.payload with a trailing dot and no signature bytes
7	kid SQL injection	kid set to ' OR '1'='1 — does it propagate to a key lookup?
8	crit unknown extension	token declaring crit:["x-custom"] with an unrecognized extension
9	Clock skew defaults	nbf in the future, exp in the past, with no tolerance configured

The libraries

Library	Ecosystem	Version
jsonwebtoken	Node.js	9.0.3
jose	Node.js	5.10.0
fast-jwt	Node.js	5.0.6
PyJWT	Python	2.13.0
python-jose	Python	3.5.0
golang-jwt	Go	v5.2.2
lestrrat-go/jwx	Go	v2.1.4
Microsoft.IdentityModel	.NET	8.18.0

Requirements

• Node.js (fixtures and runner)
• Python 3 + pip
• Go
• .NET SDK

Run the battery

From the repo root:

./runner/run-all.sh

This installs each harness's dependencies, runs every harness against the corpus, and writes result fragments to results/tmp/. It runs clean on macOS ARM64.

Read the results

runner/aggregate.js reads all fragments and writes results/matrix.json:

• library_versions — versions captured at run time
• results[variant][library] — one entry per library per variant, with three fields:
  • result — SAFE (rejected correctly) or VULNERABLE (accepted a token it should have rejected), or ERROR if the harness failed
  • note — the library's actual error message or observed behavior
  • reproducer — the harness test file that produced the entry

{
  "generated": "2026-05-31T13:27:12.308Z",
  "library_versions": {
    "jsonwebtoken": "9.0.3",
    "jose": "5.10.0"
  },
  "results": {
    "alg_confusion_rs256_hs256": {
      "jsonwebtoken": {
        "result": "SAFE",
        "note": "jsonwebtoken rejected algorithm confusion: invalid algorithm",
        "reproducer": "harnesses/node-jsonwebtoken/tests/01_alg_confusion.test.js"
      }
    }
  }
}

Re-aggregate without re-running the battery:

node runner/aggregate.js

Project structure

fixtures/     # corpus + keys (committed)
  corpus/     # one JSON file per attack variant
  keys/       # test-only RSA-2048 / EC P-256 keypairs
harnesses/    # one self-contained harness per library (Node, Python, Go, .NET)
runner/       # run-all.sh orchestration + aggregate.js
results/      # matrix.json (committed); tmp/ fragments (gitignored)
tests/        # root-level test area; each harness owns its own tests

License

MIT. See LICENSE.