CVE-2026-73576 in Collaboration
Summary
by MITRE • 08/13/2026
In Zimbra Collaboration (ZCS) before 10.1.17, weak cryptographic key generation vulnerability exists in the OnlyOffice integration. The zimbraDocumentEditingJwtSecret is generated using an insecure random number generator, resulting in insufficient entropy. An attacker who obtains a JWT signed with the generated secret may be able to recover the JWT signing secret through offline brute-force, potentially enabling JWT forgery.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability under examination involves a critical weakness in Zimbra Collaboration Suite version 10.1.16 and earlier, specifically within its OnlyOffice integration component. This issue stems from the improper implementation of cryptographic key generation mechanisms that directly impacts the security of JSON Web Token (JWT) authentication processes. The affected parameter zimbraDocumentEditingJwtSecret demonstrates a fundamental flaw in entropy generation that undermines the overall cryptographic integrity of the system. According to the weakness classification, this represents a direct violation of cryptographic best practices and falls under the category of weak random number generation as defined by CWE-330.
The technical exploitation of this vulnerability occurs through the insecure generation of JWT signing secrets used in document editing operations. When Zimbra generates these secrets, it employs a cryptographically weak random number generator that produces values with insufficient entropy to resist brute-force attacks. This weakness enables attackers to perform offline dictionary or brute-force attacks against the generated secrets, potentially recovering the private keys used for JWT signature verification. The operational impact of this flaw extends beyond simple authentication bypasses, as successful exploitation could allow unauthorized users to forge valid JWT tokens and gain elevated privileges within the document editing environment.
The security implications of this vulnerability align with several ATT&CK techniques including privilege escalation through credential access and defense evasion via token manipulation. Attackers can leverage this weakness to impersonate legitimate users within the Zimbra ecosystem, potentially accessing sensitive documents and performing unauthorized operations. The low complexity required for exploitation makes this vulnerability particularly dangerous in environments where document collaboration is prevalent and where attackers may have initial access through other vectors. Organizations using Zimbra Collaboration Suite with OnlyOffice integration face significant risk of unauthorized data access and potential compromise of entire document management workflows.
Mitigation strategies must focus on immediate remediation through the upgrade to Zimbra Collaboration Suite version 10.1.17 or later, which addresses the cryptographic implementation issues in the JWT secret generation process. System administrators should also implement monitoring for suspicious authentication patterns and JWT usage within their environments. The fix implemented by Zimbra employs a cryptographically secure random number generator that provides adequate entropy for JWT secret generation, ensuring that future secrets cannot be easily brute-forced. Additionally, organizations should consider implementing additional security controls such as rate limiting on authentication attempts and enhanced logging of document editing activities to detect potential exploitation attempts.
This vulnerability demonstrates the critical importance of proper cryptographic implementation in enterprise collaboration platforms where document integrity and user authentication are paramount. The weakness highlights how seemingly minor implementation details in random number generation can have significant security implications across an entire platform ecosystem. Organizations should conduct comprehensive audits of their cryptographic implementations, particularly focusing on entropy sources used for key generation, to identify similar vulnerabilities that may exist in other components of their infrastructure. The remediation process requires not only software updates but also verification that existing JWT tokens are invalidated and regenerated using secure methods to prevent exploitation of the vulnerability through cached or previously generated credentials.