CVE-2026-44523: Github.com/enchant97/note mark/backend Note Mark Has A JWT Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q6mh-rqwh-g786",
  "modified" : "2026-05-15T23:45:05Z",
  "published" : "2026-05-07T21:08:10Z",
  "aliases" : [ "CVE-2026-44523" ],
  "summary" : "Note Mark has a JWT Secret Weakness that allows Full Account Takeover via Token Forgery",
  "details" : "#### Summary\n\nNo minimum length or entropy is enforced on the `JWT_SECRET` configuration value. The application accepts any base64-decodable secret regardless of size, including secrets as short as 1 byte.\n\nHS256 secrets below 32 bytes are brute-forceable offline, allowing attackers to recover the signing key and forge valid JWTs for arbitrary users.\n\n---\n\n#### Impact\n\nAn attacker who captures a single valid JWT (e.g, from cookies, logs, or network traffic) can:\n\n\\> Crack the signing secret offline using brute-force or wordlist attacks\n\\> Forge valid JWTs for any user ID (including administrators)\n\\> Authenticate without knowing any credentials\n\nThis results in **full account takeover across the entire application** with no server-side detection or rate limiting possible.\n\n---\n\n#### Details\n\nIn `backend/config/utils.go`, the `Base64Decoded.UnmarshalText` function decodes the JWT secret but does not validate its length or entropy.\n\nIn `backend/core/auth.go`, JWT tokens are signed using HS256 without enforcing minimum key size requirements.\n\nAccording to **RFC 7518 Section 3.2**, HS256 keys must be at least 256 bits (32 bytes). Libraries such as PyJWT explicitly warn against shorter keys, but note-mark performs no such validation.\n\n---\n\n### PoC\n\n1- Deploy note-mark with a weak secret:\n\n   ```\n   JWT_SECRET = base64(\"testsecret123456789012345\")\n   ```\n\n2- Register an account and capture the `Auth-Session-Token` cookie\n\n3- Crack the secret offline (example using Python):\n\n   ```python\n   import jwt, base64\n   jwt.decode(TOKEN, base64.b64decode(SECRET), algorithms=[\"HS256\"])\n   ```\n\n4- Forge a new token for any user UUID with extended expiry\n\n5- Send the forged token in requests → server returns **200 Ok** and authenticates as that user\n\n---\n\n### Reproduction Steps\n\n1- Deploy the application with a JWT secret shorter than 32 bytes (after base64 decoding)\n2- Authenticate and capture a valid JWT\n3- Perform offline brute-force or dictionary attack against the token signature\n4- Recover the secret\n5- Generate a forged JWT for another user\n6- Use the forged token to access protected endpoints\n\n---\n\n### Fix Recommendation\n\n* Enforce a **minimum of 32 bytes (256 bits)** for JWT secrets after base64 decoding\n* Reject weak secrets during configuration parsing (e.g., in `Base64Decoded.UnmarshalText` or config validation)\n* Optionally log warnings or fail startup if the secret is insecure\n\n---\n\n### Resources\n\n* RFC 7518 Section 3.2 (JSON Web Algorithms - HMAC key size requirements)\n* CWE-326: Inadequate Encryption Strength\n* CWE-345: Insufficient Verification of Data Authenticity\n\n---",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/enchant97/note-mark/backend"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.0.0-20260501152247-18b587758667"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/enchant97/note-mark/security/advisories/GHSA-q6mh-rqwh-g786"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44523"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/enchant97/note-mark/commit/18b58775866776ed400c403dd0ccad68c1fa4802"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/enchant97/note-mark"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/enchant97/note-mark/releases/tag/v0.19.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-326", "CWE-345" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-07T21:08:10Z",
    "nvd_published_at" : "2026-05-14T19:16:37Z"
  }
}