CVE-2026-27802: Vaultwarden: Privilege Escalation via Bulk Permission Update to Unauthorized Collections by Manager

Summary

A Manager account (accessall=false) was able to escalate privileges by directly invoking the bulk-access API against collections that were not originally assigned to them. The API allowed changing assigned=false to assigned=true, resulting in unauthorized access.

Additionally, prior to the bulk-access call, the regular single-update API correctly returned 401 Unauthorized for the same collection. After executing the bulk-access API, the same update API returned 200 OK, confirming an authorization gap at the HTTP level.

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Description

The endpoint accepts ManagerHeadersLoose and does not validate access rights for the specified collectionIds. src/api/core/organizations.rs:551

rust headers: ManagerHeadersLoose,

The received collectionids are processed directly without per-collection authorization checks. src/api/core/organizations.rs:564

rust for colid in data.collectionids {

Existing group assignments for the collection are deleted. src/api/core/organizations.rs:583

rust CollectionGroup::deleteallbycollection(&colid, &conn).await?;

Existing user assignments for the collection are deleted. src/api/core/organizations.rs:590

rust CollectionUser::deleteallbycollection(&colid, &conn).await?;

By comparison, another bulk-processing endpoint performs per-collection validation using fromloose. src/api/core/organizations.rs:787

rust let headers = ManagerHeaders::fromloose(headers, &collections, &conn).await?;

The actual access control logic is implemented in canaccesscollection, which is not invoked in the bulk-access endpoint. src/auth.rs:911

rust if !Collection::canaccesscollection(&h.membership, colid, conn).await {

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Preconditions

The attacker possesses a valid Manager account within the target organization. The organization contains collections that are not assigned to the attacker. The attacker can authenticate through the standard API login process (Owner/Admin privileges are not required).

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Steps to Reproduce

1. Log in as a Manager and obtain a Bearer token. <img width="4016" height="1690" alt="image" src="https://github.com/user-attachments/assets/218f05e2-6a2e-4066-8f8d-6bbef1cc5858" />

2. Confirm the current values of assigned, manage, readOnly, and hidePasswords for the target collection. <img width="4026" height="1694" alt="image" src="https://github.com/user-attachments/assets/a6d2fc70-5370-4984-85bd-a6f74febdfa3" />

3. Verify that the standard update API returns 401 Unauthorized when attempting to modify the unassigned collection. <img width="4030" height="1708" alt="image" src="https://github.com/user-attachments/assets/802f0d2b-d474-44d2-beef-b4f7f3335225" />

4. Invoke the bulk-access API, including: <img width="4036" height="1120" alt="image" src="https://github.com/user-attachments/assets/1d3caa01-3ac2-4636-9ed0-189e5923c986" />

collectionIds containing the target collection users containing the attacker’s own membershipid Confirm that the API returns 200 OK.

5. Re-run the standard update API. Confirm that it now succeeds and that the previously unauthorized modification is applied. <img width="4040" height="1440" alt="image" src="https://github.com/user-attachments/assets/340e9676-d802-404c-b894-9986a176360a" />

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Required Minimum Privileges

Manager role within the target organization (the issue occurs even when accessall=false)

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Attack Scenario

A delegated administrator or department-level Manager within an organization directly calls the API to add themselves to unauthorized collections and gain access to confidential information.

Because the bulk update process deletes and reassigns existing permissions, the attacker can also remove other users’ access, enabling denial-of-service or sabotage within the organization.

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Potential Impact

Confidentiality: Unauthorized access to sensitive information within restricted collections. Integrity: Unauthorized modification of collection permission settings and arbitrary changes to access controls. Availability: Deletion of existing assignments may cause legitimate users to lose access.