{"id":"GHSA-q6mh-rqwh-g786","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\\\u003e Crack the signing secret offline using brute-force or wordlist attacks\n\\\u003e Forge valid JWTs for any user ID (including administrators)\n\\\u003e 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---","aliases":["CVE-2026-44523","GO-2026-5567"],"modified":"2026-06-25T23:11:46.726627387Z","published":"2026-05-07T21:08:10Z","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"},"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"}],"affected":[{"package":{"name":"github.com/enchant97/note-mark/backend","ecosystem":"Go","purl":"pkg:golang/github.com/enchant97/note-mark/backend"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.0.0-20260501152247-18b587758667"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-q6mh-rqwh-g786/GHSA-q6mh-rqwh-g786.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N"}]}