GHSA-5cwg-6vw7-rj6p - Forge: AES-GCM authentication bypass via unvalidated tagLength option

### Summary The AES-GCM mode in forge.cipher does not validate the tagLength option passed to start(). With a tagLength of 0 or a value that converts to 0 (such as null, false, '' or '0'), the authentication tag is empty, and decipher.finish() returns true for any ciphertext and additional data when the supplied tag is empty or missing. Fixed in node-forge 1.4.1. ### Details `modes.gcm.prototype.start()` in `lib/cipherModes.js` stored the `tagLength` option without validation, and `lib/cipher.js` documented it as accepting "0-128". After processing the data, `afterFinish()` truncates the 16-byte tag with `truncate(16 % (tagLength / 8))`. For a `tagLength` that converts to 0, this is `16 % 0 = NaN`, and truncating by `NaN` empties the tag. On decryption, the start-time check that the supplied `tag` has `tagLength / 8` bytes passes for an empty tag, and the final tag comparison compares two empty strings, so `decipher.finish()` returns `true` for any ciphertext and additional data. NIST SP 800-38D section 5.2.1.2 allows only tag lengths of 128, 120, 112, 104 and 96 bits, plus 64 and 32 bits for certain applications. The fix validates `tagLength` in `start()`, for both encryption and decryption. A missing, `null` or `undefined` `tagLength` uses the default of 128 bits. Any other value is converted with `Number()` and must be one of 128, 120, 112, 104, 96, 64 or 32; otherwise `start()` throws "Invalid tag length.". Numeric strings such as `'128'` are still accepted. With a validated `tagLength`, an empty tag no longer matches the expected tag length and is rejected. ### Patches Fixed in node-forge 1.4.1. `cipher.start()` now throws an error unless `tagLength` is one of the tag lengths allowed by NIST SP 800-38D (128, 120, 112, 104, 96, 64 or 32 bits); a `null` or `undefined` `tagLength` means the default of 128 bits. ### Workarounds Do not derive `tagLength` from received data. Pass a fixed `tagLength` (or omit it to use the default of 128 bits), and check that t