CVE-2026-72688 in OpenSignServer
Summary
by MITRE • 08/10/2026
A missing authentication vulnerability in OpenSignLabs opensignserver through 2.37.0 allows an unauthenticated remote attacker to read arbitrary stored documents via the fileupload Parse cloud function. The function mints MASTER_KEY-signed file access tokens for any caller-supplied URL without performing any session check, defeating the only access control protecting stored contract files.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability under examination represents a critical authentication bypass flaw in OpenSignLabs opensignserver version 2.37.0 and earlier, which fundamentally undermines the security posture of the system by allowing unauthenticated remote attackers to access sensitive stored documents. This weakness resides within the fileupload Parse cloud function, which serves as a critical interface for document handling within the platform's architecture. The vulnerability manifests through the function's improper implementation of access control mechanisms, specifically failing to validate session authenticity before generating access tokens for file retrieval operations.
The technical implementation of this flaw demonstrates a severe failure in the authentication flow where the MASTER_KEY-signed file access tokens are generated without any verification of caller credentials or session state. This design flaw creates a condition where any remote attacker can supply arbitrary URLs to the vulnerable function and receive valid access tokens that grant read access to stored contract files. The vulnerability operates at the application layer, exploiting improper input validation and authentication checks within the Parse cloud function implementation. According to CWE-287, this represents an inadequate authentication mechanism where system-level privileges are granted without proper verification of user identity or session legitimacy.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it enables attackers to potentially extract sensitive contractual information that may contain personal data, financial records, or proprietary business information. The remote nature of the attack means that threat actors can exploit this weakness from any network location without requiring physical access or prior credentials. This vulnerability directly violates fundamental security principles outlined in the NIST Cybersecurity Framework, particularly concerning the protection of system resources and the prevention of unauthorized access to sensitive data.
The exploitation of this vulnerability aligns with tactics described in the MITRE ATT&CK framework under the T1078 credential access category, where attackers leverage weaknesses in authentication mechanisms to gain unauthorized access to systems. The attack vector specifically corresponds to T1190-Exploit Public-Facing Application, as it targets a publicly exposed cloud function that serves as an entry point for unauthorized data extraction. This vulnerability also falls under the broader category of T1213-Data from Information Repositories, representing a direct method for extracting stored data from information repositories without proper authorization.
Organizations utilizing affected versions of OpenSignLabs opensignserver face significant risk exposure from this vulnerability, particularly in environments where sensitive contract data is stored. The lack of session validation creates a persistent threat vector that remains active until the underlying implementation is corrected, making it an attractive target for attackers seeking to access confidential business information. Security teams should implement immediate monitoring and logging of file access patterns to detect potential exploitation attempts, while also prioritizing the deployment of patches or workarounds that address the core authentication bypass issue.
The recommended mitigations include implementing proper session validation checks within the Parse cloud function before generating access tokens, ensuring that all requests undergo appropriate authentication verification before granting access to stored documents. Additionally, organizations should consider implementing rate limiting and access control restrictions on the fileupload endpoint to prevent automated exploitation attempts. The fix should address the fundamental design flaw by requiring valid user sessions or API keys for token generation, aligning with security best practices outlined in OWASP Top Ten and the ISO 27001 information security management standards. Organizations must also perform comprehensive security reviews of similar cloud functions to identify and remediate comparable authentication bypass vulnerabilities within their application infrastructure.