CVE-2016-6597 in EAS Proxy
Summary
by MITRE
Sophos EAS Proxy before 6.2.0 for Sophos Mobile Control, when Lotus Traveler is enabled, allows remote attackers to access arbitrary web-resources from the backend mail system via a request for the resource, aka an Open Reverse Proxy vulnerability.
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Analysis
by VulDB Data Team • 09/13/2022
The vulnerability identified as CVE-2016-6597 represents a critical open reverse proxy flaw in Sophos EAS Proxy versions prior to 6.2.0, specifically when integrated with Lotus Traveler functionality. This issue arises from inadequate input validation and access control mechanisms within the proxy server implementation, creating a significant security risk that allows unauthorized remote access to internal backend systems. The vulnerability specifically affects organizations using Sophos Mobile Control solutions where Lotus Traveler services are enabled, making it particularly concerning for enterprises relying on mobile device management platforms.
The technical exploitation of this vulnerability occurs through crafted HTTP requests that bypass the intended proxy filtering mechanisms. Attackers can construct malicious requests that target internal resources within the organization's network, effectively using the Sophos EAS Proxy as an open relay to access backend mail systems and other internal services. This type of vulnerability falls under CWE-444, which specifically addresses improper handling of HTTP requests, and represents a classic example of an open proxy vulnerability that enables attackers to perform unauthorized network reconnaissance and data exfiltration activities. The flaw exists because the proxy server fails to properly validate and sanitize the target URLs in incoming requests, allowing direct forwarding to internal destinations without proper authorization checks.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with the ability to conduct network reconnaissance, escalate privileges, and potentially exfiltrate sensitive data from internal mail systems. Organizations using affected versions of Sophos Mobile Control are exposed to significant risks including email content interception, user credential harvesting, and potential lateral movement within the network infrastructure. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it an attractive target for automated scanning tools and malicious actors seeking to compromise enterprise email infrastructure. This aligns with ATT&CK technique T1071.004, which describes the use of application layer protocol communication for data exfiltration and reconnaissance activities.
Mitigation strategies for CVE-2016-6597 require immediate implementation of the vendor-provided security patches and updates to Sophos EAS Proxy versions 6.2.0 and later. Organizations should also implement additional network-level controls including firewall rules that restrict access to internal mail servers from the proxy server, and implement strict URL filtering policies to prevent forwarding to internal resources. Network segmentation and access control lists should be configured to ensure that the proxy server can only access authorized external resources while maintaining proper isolation from internal backend systems. Security teams should also conduct thorough network monitoring to detect any suspicious proxy activity and implement intrusion detection systems to identify potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and access control implementation in network security appliances, as highlighted in industry best practices for secure proxy server configuration and the principles outlined in the OWASP Top Ten security framework.