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Unauthorized Access via Partial Update API on Another User’s Cipher

Moderate
dani-garcia published GHSA-w9f8-m526-h7fh Mar 4, 2026

Package

cargo vaultwarden (Rust)

Affected versions

1.35.3

Patched versions

1.35.4

Description

Summary

An authenticated regular user can specify another user’s cipher_id and call the following API:

PUT /api/ciphers/{id}/partial

Although the standard retrieval API correctly denies access to the target cipher, this partial update endpoint returns 200 OK and includes information such as cipherDetails (name, notes, data, secureNote, etc.) in the response.


Impact

  • Retrieval of another user's encrypted cipher information
  • Creation of unauthorized associations within the attacker's user context (e.g., favorite or folder operations)

In addition, the response from /api/ciphers/<cipher_id>/partial contains attachments[].url.

For filesystem (FS) deployments, the following tokenized endpoint is returned:

/attachments/<cipher>/<file>?token=...

For object storage deployments, a short-lived pre-signed URL is returned.

As a result, an attacker can use these URLs to directly download attachment data that they are not authorized to access.

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVE ID

CVE-2026-27898

Weaknesses

Authorization Bypass Through User-Controlled Key

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. Learn more on MITRE.

Credits