SiYuan: Anonymous publish-password authentication bypass via getHeadingChildrenDOM / getHeading*Transaction / getBacklinkDoc (publish mode)

QFinch assessment

SiYuan's publish mode defines a "protected" access level: a document that is publicly listed but requires a password to read (per the product's own UI help text, protected = "Publicly visible, requires password to access"). The password is enforced on the primary content path (getDoc, via FilterContentByPublishAccess). Several other content-returning endpoints getHeadingChildrenDOM, getHeadingDeleteTransaction/getHeadingLevelTransaction/ getHeadingInsertTransaction, and getBacklinkDoc/getBackmentionDoc return rendered block DOM with no password check at all. Combined with reader-reachable endpoints that leak a protected document's internal block IDs, an anonymous reader can retrieve the full body of a password-protected document without the password. This has been reproduced end-to-end on a live instance.

Potential impact

An anonymous reader (publish mode with auth disabled) or any publish RoleReader can read the full content of a password-protected published document without the password, defeating the "protected" access control the product documents as a password gate. The core defect is that these content-returning endpoints perform no publish-password check; the ID-leak endpoints (multiple sources) supply the block IDs that make the bypass reachable anonymously and untargeted. Impact is confidentiality-only (content disclosure); no modification occurs on these paths. Encrypted notebooks are out of scope.

Technical context

The password control and where it is enforced. Publish access has five levels encoded in visible/password/disable: public, protected (password), hidden, private (password), forbidden. getDoc correctly enforces the password for protected/private documents via FilterContentByPublishAccess. The bug is that other content endpoints do not. Content endpoints with no password check (all CheckAuth-only): - getHeadingChildrenDOM returns rendered DOM of a heading subtree. - getHeadingDeleteTransaction/getHeadingLevelTransaction/getHeadingInsertTransaction return rendered heading DOM in the computed transaction payload (no mutation occurs on this path). - getBacklinkDoc/getBackmentionDoc return rendered DOM of referencing blocks. None of these invokes the publish-password check that getDoc applies. Each converts a block ID into full rendered content regardless of the containing document's protected/password status. The ID-leak that removes the precondition. A protected document is, by design, publicly listed (listDocsByPath filters on visible, and protected documents are visible), so an anonymous reader obtains the document's root ID. The document's internal block/heading IDs are then obtainable from reader-reachable endpoints notably the searchEmbedBlock endpoint (reported separately), whose post-query filter FilterEmbedBlocksByPublishAccess replaces the content string but retains the block ID. So the "filtered" search still yields the protected document's internal heading IDs. (Other reader-reachable endpoints also leak block IDs, the vulnerability does not depend on any single ID source.) The chain, reproduced on a live instance. Against a real protected document (password set), an anonymous reader on port 6808 with no token and no password: 1. getDoc(protectedDoc) → returns the password-required placeholder (correctly blocked). 2. searchEmbedBlock with a statement selecting heading blocks for the document's root ID → returns the heading IDs (content filtered, IDs retained). 3. getHeadingChildrenDOM(headingId) → returns the full rendered body of the protected document, including its protected content. The password gate that step 1 enforces is entirely bypassed by step 3.