CVE-2026-87879 in Cyber Protect
Summary
by MITRE • 10/28/2026
Sensitive information disclosure due to improper token validation. The following products are affected: Acronis Cyber Protect 17 (Linux, Windows) before build 42587.
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability in question represents a critical failure in the authentication and session management mechanisms of Acronis Cyber Protect versions prior to build 42587 for both Linux and Windows platforms. This flaw stems from improper validation of security tokens, which are essential components used to verify user identity and authorize access to sensitive system resources. In modern web-based administrative interfaces or API endpoints, tokens such as JSON Web Tokens (JWT) or session cookies serve as the primary means of maintaining stateless authentication across requests. When these tokens are not rigorously validated upon receipt by the server, an attacker can exploit this lapse to bypass intended security controls and gain unauthorized access to protected functionalities.
From a technical perspective, improper token validation typically involves several potential failure modes that may be present in the affected software architecture. These include accepting expired or revoked tokens without re-authentication, failing to verify cryptographic signatures which allows for tampering with payload data, or neglecting to validate audience and issuer claims which permits cross-service impersonation attacks. In the context of Acronis Cyber Protect, this deficiency likely affects the administrative console where backup policies, system configurations, and sensitive data access are managed. If an attacker can forge a valid-looking token or reuse a previously captured one that was not properly invalidated by the server-side logic, they effectively bypass the authentication layer entirely. This type of flaw is categorized under CWE-287 Improper Authentication within the Common Weakness Enumeration framework, highlighting a fundamental breakdown in verifying user identity before granting access to protected resources.
The operational impact of this vulnerability is severe due to the privileged nature of the Acronis Cyber Protect platform. As an enterprise-grade solution for data protection and endpoint security management, it holds deep integration with operating systems, databases, and network infrastructure. Unauthorized access resulting from token validation failures could allow a malicious actor to exfiltrate sensitive backup archives containing proprietary business information, customer records, or intellectual property. Furthermore, the attacker might manipulate backup schedules to delete critical recovery points, effectively enabling ransomware-style attacks by removing defenses before deployment of malware. The ability to alter system configurations without authorization also poses significant risks for lateral movement within a network, as compromised administrative credentials can be used to pivot to other systems that trust the Acronis management infrastructure.
This vulnerability aligns with several tactics and techniques defined in the MITRE ATT&CK framework. Specifically, it relates to T1078 Valid Accounts, where attackers use legitimate but improperly validated credentials or tokens to maintain persistence without triggering typical intrusion detection alerts. It also intersects with T1539 Steal Web Session Cookie if session cookies are involved, and potentially T1496 Resource Hijacking if the compromised access is used for cryptomining or other resource-intensive activities disguised as normal administrative tasks. The lack of robust token validation means that traditional perimeter defenses may not detect these unauthorized actions because they appear to originate from authenticated sessions, making detection reliant on behavioral analytics rather than simple signature matching.
Mitigation strategies must focus immediately on updating the affected software to build 42587 or later, where the vendor has presumably implemented stricter token verification protocols including expiration checks, cryptographic integrity validation, and proper session invalidation upon logout or privilege changes. In environments where immediate patching is not feasible due to operational constraints, temporary compensating controls should be deployed. These include restricting access to the administrative interface through network segmentation so that only trusted management stations can reach it, implementing Web Application Firewalls configured to detect anomalous token patterns such as unusual expiration dates or malformed signatures, and enabling enhanced logging for authentication events to monitor for signs of token reuse or forgery attempts. Additionally, organizations should review their session timeout policies to ensure that tokens do not remain valid indefinitely, reducing the window of opportunity for exploitation if a token is compromised through other vectors like cross-site scripting attacks on older client-side components.