JWT bug let anyone impersonate Mnemosyne memory users

A JWT bug let anyone impersonate any user of mnemosyne-memory, the sync server behind an agent memory system. The GitHub Advisory Database entry, published September 18, rates it 9.1 and covers every release up to and including v3.10.0.

The stakes are direct: an unauthenticated attacker with network access could read or rewrite another user's stored agent memory, no credentials required. That's not a profile field or a shopping cart. It's the context an agent carries across sessions, and a forged token handed over both read and write access to it.

The server took bearer tokens, base64-decoded them, then called a JWT library with options that turned off signature verification. Any well-formed token got accepted, including ones using alg:none, which carries no signature at all. Forge a token with a target user_id and the server does the rest.

The fix in v3.10.1 replaces the decode-and-trust path with a stdlib HS256 verifier. It uses hmac.compare_digest for the comparison, a strict algorithm check, and UTC-aware expiration validation. That's the boring, correct way to check a signature.

The advisory doesn't say how long v3.10.0 ran in production before the fix, or whether anyone can confirm it was exploited before the patch. If you're running mnemosyne-memory, v3.10.1 is the version to be on.