GHSA-4g37-7p2c-38r9: Open WebUI Vulnerable to IDOR: Retrieval API Bypasses Knowledge Base Access Controls
IDOR: Retrieval API Bypasses Knowledge Base Access Controls**Author:** Andrew Orr <aorr@tenable.com>Summary`_validate_collection_access()` ([PR #22109](https://github.com/open-webui/open-webui/pull/22109)) checks the `user-memory-*` and `file-*` collection name prefixes but does not check knowledge base collections, which use raw UUIDs as collection names. Any authenticated user who knows a private knowledge base UUID can read its content through the retrieval query endpoints, even though the knowledge API correctly denies that user access. The same gap affects the retrieval write endpoints (`/process/text`, `/process/file`, `/process/files/batch`, `/process/web`, `/process/youtube`), allowing an attacker to inject content into or overwrite another user's knowledge base.Reproduced on `main` at commit `4d058a125` (v0.8.11) on March 26, 2026.SeverityCWE-639: Authorization Bypass Through User-Controlled KeyCVSS 3.1: `7.5 (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H)` -- `AC:H` because exploitation requires knowing a target UUID; `I:H` and `A:H` because the write path allows poisoning or destruction of another user's knowledge baseDefault Configuration ReachabilityReachable in default configuration. All affected endpoints require only `get_verified_user`, not `get_admin_user`, so any non-admin account in a typical multi-user deployment can reach them. The only prerequisite beyond authentication is knowledge of a target knowledge base UUID, which is reflected in the `AC:H` score. However, KB UUIDs are stable identifiers that leak through normal usage rather than secrets (see Prerequisites below).Root CauseKnowledge base embeddings are stored in vector DB collections named with the knowledge base's UUID (e.g., `550e8400-e29b-41d4-a716-446655440000`). The `_validate_collection_access` function only blocks two specific prefixes:Knowledge base UUIDs do not match either prefix, so the function returns without raising an exception. The query then executes against the vector DB with no further authorization check.Vulnerable EndpointsRead EndpointsBoth retrieval query endpoints accept a collection name and call `_validate_collection_access` as their sole authorization gate:`POST /api/v1/retrieval/query/doc` (line 2367) -- single `collection_name``POST /api/v1/retrieval/query/collection` (line 2432) -- list of `collection_names`Write EndpointsThe following endpoints accept a `collection_name` parameter and write to the target collection without checking whether the caller owns it:`POST /api/v1/retrieval/process/text` (line 1777) -- appends attacker-controlled content to the target collection`POST /api/v1/retrieval/process/file` (line 1528) -- validates ownership of the uploaded file but not the destination collection`POST /api/v1/retrieval/process/files/batch` (line 2578) -- same as above for multiple files`POST /api/v1/retrieval/process/web` and `POST /api/v1/retrieval/process/youtube` (lines 1810-1811) -- same handler; `overwrite` defaults to `true`, so targeting an existing knowledge base deletes and replaces it| Endpoint | Read | Write | Overwrite | Access Check |
|----------|------|-------|-----------|--------------|
| /query/doc | Yes | -- | -- | Prefix-only (bypassed) |
| /query/collection | Yes | -- | -- | Prefix-only (bypassed) |
| /process/text | -- | Yes | -- | None |
| /process/web | -- | Yes | Yes (default) | None |
| /process/youtube | -- | Yes | Yes (default) | None (same handler as /process/web) |
| /process/file | -- | Yes | -- | File only, not collection |
| /process/files/batch | -- | Yes | -- | File only, not collection |Proof of Concept**Security boundary crossed:** The knowledge base access control system (ownership checks, group-based access grants) is bypassed at the retrieval layer. A non-admin user who knows a private knowledge base UUID can read it, append attacker-controlled content to it, or destroy and replace it through the retrieval API, even though the knowledge API correctly denies the same user access to the same resource.`open-webui-idor-poc.sh` provides a self-contained Docker lab that stands up the target environment and tests every vulnerable endpoint listed above. See the comments at the top of that file for setup, usage, and configuration options.PrerequisitesAttacker has an authenticated (non-pending) account on the target instance.A victim user has created a private knowledge base containing sensitive documents.Attacker knows the victim's knowledge base UUID. V4 UUIDs are not guessable, but they are stable identifiers that leak through normal platform usage:**Access revocation:** A user learns a KB UUID through a shared workspace or group, loses access, and finds the retrieval API still honors the stale UUID. The knowledge API correctly revokes access at request time (`access_grants.py:549-558` dynamically queries current group memberships), but the retrieval API has no equivalent check.**Model metadata:** When a model is shared with a group, `GET /api/models/list` returns the full `meta.knowledge` array -- including KB UUIDs -- to every user with access to the model, even if they have no access to the referenced knowledge bases (`models.py:58-130`).**URL leakage:** KB UUIDs appear in browser URLs (`/workspace/knowledge/{id}`, `Knowledge.svelte:260`) and can leak through shared links, browser history, Referrer headers, or proxy logs.**RAG citation metadata:** KB UUIDs are stored as `source.id` in chat message sources (`middleware.py:1950-1965`, `socket/main.py:880-897`). Shared chats return these sources unfiltered (`chats.py:815-830`).Read: Extract Private KB ContentAuthenticate as the attacker:**Control request:** the knowledge API correctly blocks the attacker:**Exploit request:** the retrieval API returns the same KB's content without authorization:Expected result when vulnerable: the server returns matching document chunks from the victim's private knowledge base, including text content and metadata (source filenames, file IDs, hashes).The `/query/collection` endpoint accepts a list of collection names and behaves identically:Write: File Injection via /process/fileThe `/process/file` endpoint validates that the attacker owns the uploaded file but does not validate the target `collection_name`. The attacker uploads a file under their own account, then processes it into the victim's collection:Write: Batch File Injection via /process/files/batchSame pattern as above but accepts multiple files in a single request:Write: Text Injection via /process/text`/process/text` appends attacker-controlled content to an existing knowledge base collection:The PoC then verifies that the injected text is returned by a follow-up query against the victim collection.Write: YouTube Transcript Replacement via /process/youtube`/process/youtube` uses the same handler as `/process/web` with the same `overwrite=true` default. This request replaces the victim's collection with the fetched transcript:Write: Data Destruction via /process/web`/process/web` defaults to `overwrite=true`, which deletes the existing collection before writing. The explicit query string below makes the destructive behavior obvious:Impact**Confidentiality**: Any authenticated user can read private knowledge base contents belonging to other users on the instance.**Integrity**: Attacker-controlled content can be injected into another user's knowledge base, poisoning downstream RAG results. Injected prompt-injection payloads would be passed to the model when the victim queries the knowledge base.**Availability**: `/process/web` and `/process/youtube` default to `overwrite=true`, letting an attacker delete and replace a victim's entire knowledge base in a single request.RemediationTwo changes are needed:Add a `permission` parameter to `_validate_collection_access`, use it for both `file-*` and knowledge base checks, and add a knowledge base ownership/access check for collection names that do not match the existing prefixes. `AccessGrants.has_access` already resolves group memberships internally when `user_group_ids` is omitted, matching the pattern used throughout `knowledge.py`.The affected write endpoints must call `_validate_collection_access` with `permission="write"` before operating on the provided `collection_name`.The existing read callers (`/query/doc`, `/query/collection`) use the default `permission="read"` and require no change. Each affected write endpoint needs a validation call after `collection_name` is resolved:`/process/text` (line 1777):`/process/web` and `/process/youtube` (lines 1810-1811, same handler):`/process/file` (line 1528):`/process/files/batch` (line 2578):Regression TestA regression test should verify that `_validate_collection_access` blocks non-owners from accessing knowledge base collections:For additional coverage, maintainers may want an integration test that creates a knowledge base as one user and confirms that a second user's retrieval query is rejected end-to-end.AI DisclosureAI assistance was used to help analyze the code paths, develop the PoC workflow, and draft this report.Attachments[open-webui-idor-poc.log](https://github.com/user-attachments/files/26283199/open-webui-idor-poc.log)
[open-webui-idor-poc.sh](https://github.com/user-attachments/files/26283201/open-webui-idor-poc.sh)Tenable's Disclosure PolicyTenable follows a 90-day vulnerability disclosure policy. That means, even though we prefer coordinated disclosure, we'll issue an advisory on June 24, 2026 with or without a patch. Alternatively, any uncoordinated vendor release of a patch or advisory to any customers before the 90-day deadline will be considered public disclosure, and Tenable may release an advisory prior to the coordinated disclosure date. Please read the full details of our policy here: https://static.tenable.com/research/tenable-vulnerability-disclosure-policy.pdfThank you for taking the time to read this. We'd greatly appreciate it if you'd acknowledge receipt of this report. If you have any questions we'd be happy to address them.
CVSS v3.1: 7.5