CVE-2026-66306 in Skype for Business Server
Summary
by MITRE • 09/08/2026
Generation of error message containing sensitive information in Skype for Business allows an unauthorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified involves the improper generation and transmission of error messages within Microsoft Skype for Business, which inadvertently exposes sensitive internal system information to external parties. This flaw represents a classic instance of Information Exposure through Error Handling, categorized under CWE-209 in the Common Weakness Enumeration standard. The core technical issue lies in the application's failure to sanitize or abstract diagnostic data before it is returned to the client during error conditions. When an unauthorized attacker interacts with the service by triggering specific malformed requests or exploiting edge cases in protocol handling, the server responds with detailed stack traces, internal IP addresses, database query structures, or configuration paths rather than generic, user-friendly error messages. This behavior violates fundamental security principles regarding the principle of least privilege and minimal information disclosure, as it provides an attacker with a roadmap to further refine their exploitation strategies against the target infrastructure.
From an operational perspective, this vulnerability significantly lowers the barrier for subsequent attacks by facilitating reconnaissance activities. An adversary can leverage these detailed error messages to map the internal network topology, identify specific software versions running on backend servers, and locate sensitive endpoints that may be vulnerable to other known exploits such as SQL injection or remote code execution. This aligns with the ATT&CK technique T1059 Command and Scripting Interpreter for gathering system information via automated tools that parse error responses, as well as T1482 Domain Trust Discovery if internal trust relationships are revealed through network-level errors. The disclosure of sensitive data over a network allows an unauthenticated attacker to gain valuable intelligence without needing direct access to the application's functional features, effectively turning standard operational feedback into a powerful reconnaissance vector that can lead to full system compromise or significant data breaches depending on the sensitivity of the exposed details.
Mitigation strategies for this vulnerability require both immediate technical fixes and long-term architectural changes. The primary remediation involves implementing strict input validation and output encoding mechanisms within the Skype for Business application codebase to ensure that error responses are standardized and stripped of any internal diagnostic information before being transmitted over the network. Developers must adopt a defensive programming approach where all exceptions are caught at higher levels in the call stack, logged securely on the server side with full context, but only generic messages such as Internal Server Error or Bad Request are returned to the client. Additionally, organizations should configure their web servers and application firewalls to intercept and replace verbose error pages with custom, sanitized templates that do not reveal underlying technology stacks or internal paths. Regular security audits and penetration testing focused on information leakage through error handling mechanisms are essential to ensure that such vulnerabilities remain patched as new features are added to the platform.