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CVE-2026-72691 – Authentication Bypass – OpenSign (OpenSignLabs opensignserver) versions up to and i

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Summary

CVE-2026-72691 is an authentication bypass vulnerability (CWE-288) in OpenSignLabs opensignserver through version 2.37.0. An unauthenticated, remote attacker can mint MASTER_KEY-signed file access tokens for arbitrary stored files via the getsignedurl Parse cloud function, resulting in disclosure of confidential documents. It is rated High severity (CVSS v3.1 base score 7.5).

Technical details

  • Root cause: The getsignedurl Parse cloud function skips its isAuthenticated check whenever a docId parameter is supplied — even a value that references no real document.
  • Trigger conditions: An attacker supplies an arbitrary string as the docId parameter, bypassing the authentication gate without any valid credentials or session.
  • Attack vector: Network; no authentication, privileges, or user interaction required.
  • Impact: The function mints MASTER_KEY-signed file access tokens for arbitrary stored files, allowing an unauthenticated attacker to read confidential stored documents (high confidentiality impact; no integrity or availability impact).

Affected software

  • OpenSignLabs opensignserver: all versions from 0 up to and including 2.37.0.

Severity

  • CVSS v3.1 base score: 7.5 (High)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade opensignserver to a release later than 2.37.0 once available from the vendor, and monitor the official OpenSign repository for the fixed release.
  • If no patch: Restrict network exposure of the opensignserver instance and its Parse cloud function endpoints, placing them behind authenticated gateways or IP allowlisting, and limit internet accessibility of the getsignedurl endpoint until an updated version can be deployed.

References

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