SiYuan: Encrypted-notebook key-derivation material and wrapped notebook keys disclosed to anonymous readers, enabling offline master-password cracking

CVE: This vulnerability corresponds to CVE-2026-72801.

Summary

Two CheckAuth-only endpoints disclose the complete offline attack material for the encrypted-notebook master password, plus the wrapped per-notebook key needed to use it. Both are reachable by the publish RoleReader token and by the anonymous account when Publish.Auth.Enable is false. An unauthenticated remote client can retrieve the Argon2id salt and cost parameters, a verifier that confirms a correct password offline, and the encrypted per-notebook data key reducing the security of every encrypted notebook to the master password's resistance to offline GPU cracking.

Details

(1) POST /api/system/getConf leaks NotebookCrypto.

getConf → GetMaskedConf() marshals the full configuration including NotebookCrypto *conf.NotebookCrypto (JSON tag notebookCrypto, not -, so it survives the deep copy). For non-administrators HideConfSecret() is applied, which nulls a dozen secret-bearing fields like AI, MCPOAuth, Api, Flashcard, Publish, Repo, Sync, Secrets, Variables, System paths but contains no reference to NotebookCrypto. FilterConfByPublishIgnore() for readers only touches UILayout.

The reader therefore receives:

Either KEKVerifier or KEKMAC is a self-contained offline oracle:

KEK = Argon2id(guess, MasterSalt, KDFParams)
correct if AES-GCM-decrypt(KEKVerifier, VerifierNonce) == magic
        or HMAC(KEK) == KEKMAC

No server round-trips are required, so there is no rate limiting, lockout, or logging on guesses, and the work is fully GPU-parallelisable.

(2) POST /api/notebook/getNotebookConf leaks the wrapped data key.

box.GetConf() returns the full BoxConf including BoxCrypt.WrappedDEK, the per-notebook data-encryption key wrapped under the KEK via AES-GCM together with WrapNonce. getNotebookInfo is the same class. Once (1) yields the master password, the attacker derives the KEK, decrypts WrappedDEK to recover the real data-encryption key, and decrypts every .sy file in that notebook.

Why this matters beyond the at-rest threat model. Storing verifier and KDF material alongside the ciphertext is reasonable against a local attacker who already has filesystem access. Serving MasterSalt + KDFParams + KEKVerifier + WrappedDEK to an anonymous remote reader converts that at-rest assumption into a remote pre-authentication cracking opportunity.

Guarded-sibling asymmetry. HideConfSecret nulls a dozen secret fields but omits NotebookCrypto. lsNotebooks filters notebook visibility for readers, while getNotebookConf and getNotebookInfo apply no reader filter at all.

Verified at origin/master (eef105683): handler bodies as described; HideConfSecret contains zero NotebookCrypto matches; FilterConfByPublishIgnore touches only UILayout; all relevant struct JSON tags are non--; all three routes are registered CheckAuth without CheckAdminRole.

Proof of Concept

Precondition: publish mode enabled (default port 6808) with at least one encrypted notebook configured; anonymous when Publish.Auth.Enable is false, otherwise any publish reader account.

1. Retrieve the key-derivation material as an anonymous reader:

POST http://127.0.0.1:6808/api/system/getConf
{}

The response's notebookCrypto object contains MasterSalt, KDFParams, KEKVerifier, VerifierNonce, and KEKMAC while the same response has the other secret fields (Api, Repo, Sync, Publish, System paths) correctly blanked, demonstrating the omission.

2. Retrieve the wrapped notebook key:

POST http://127.0.0.1:6808/api/notebook/getNotebookConf
{"notebook":"<NOTEBOOK_ID>"}

The response contains BoxCrypt.WrappedDEK and WrapNonce.

3. Offline: candidate passwords are verified locally against KEKVerifier/KEKMAC using MasterSalt and KDFParams, with no further server interaction. A recovered password yields the KEK, which unwraps WrappedDEK to the notebook's data-encryption key.

Verification status: the leak paths are confirmed by code inspection at origin/master. A live end-to-end demonstration requires a build from HEAD with an encrypted notebook enabled; the test instance available predates the encrypted-notebook feature, so no runtime reproduction is claimed here.

Impact

An unauthenticated remote client (publish mode with auth disabled) or any publish RoleReader obtains everything needed to mount an unlimited, unthrottled, GPU-parallel offline attack on the encrypted-notebook master password, plus the wrapped data key to decrypt notebook contents once the password is recovered. The confidentiality of every encrypted notebook then rests solely on master-password entropy against an offline attacker, rather than on the password remaining unknown to remote parties. No rate limiting or detection applies, because guessing occurs entirely off-server.

Suggested fix

• In HideConfSecret, replace NotebookCrypto with a minimal {enabled: bool} for non-administrators the frontend only needs the enabled flag for the lock UI stripping MasterSalt, KDFParams, KEKVerifier, VerifierNonce, and KEKMAC.
• Apply reader filtering to getNotebookConf and getNotebookInfo so BoxCrypt (including WrappedDEK and WrapNonce) is omitted for non-administrator roles.