CVE-2017-2836 in FreeRDP
Summary
by MITRE
An exploitable denial of service vulnerability exists within the reading of proprietary server certificates in FreeRDP 2.0.0-beta1+android11. A specially crafted challenge packet can cause the program termination leading to a denial of service condition. An attacker can compromise the server or use man in the middle to trigger this vulnerability.
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Analysis
by VulDB Data Team • 03/07/2023
The vulnerability described in CVE-2017-2836 represents a critical denial of service weakness within the FreeRDP 2.0.0-beta1+android11 implementation that specifically targets the proprietary server certificate reading functionality. This issue stems from inadequate input validation and error handling mechanisms within the remote desktop protocol client implementation, creating a scenario where maliciously crafted challenge packets can trigger abrupt program termination. The vulnerability manifests during the certificate processing phase of the RDP connection establishment, where the software fails to properly handle malformed or specially constructed certificate data, leading to uncontrolled application crashes and service disruption.
The technical flaw resides in the certificate parsing logic that lacks proper boundary checks and validation routines when processing proprietary server certificates. This weakness falls under the CWE-129 category of Improper Validation of Array Index, as the software does not adequately verify the integrity and structure of certificate data before attempting to parse it. The vulnerability operates at the protocol level where the RDP client receives challenge packets containing certificate information, and the failure occurs when these packets contain unexpected data patterns that cause buffer overflows or invalid memory access conditions. The specific nature of the flaw suggests that the implementation does not employ robust exception handling or input sanitization measures during certificate validation.
From an operational impact perspective, this vulnerability creates significant security and availability concerns for systems relying on FreeRDP for remote desktop connections. An attacker positioned in a man-in-the-middle scenario can exploit this weakness to repeatedly send malformed challenge packets, causing the target server or client application to crash and restart continuously. This creates a persistent denial of service condition that can severely impact business operations, particularly in enterprise environments where remote access is critical for system administration and user connectivity. The vulnerability also poses indirect security risks as it can be leveraged to disrupt legitimate service availability and potentially mask other attack vectors.
The mitigation strategies for CVE-2017-2836 should focus on implementing comprehensive input validation and robust error handling mechanisms within the certificate processing pipeline. System administrators should prioritize updating to patched versions of FreeRDP that address the specific certificate parsing vulnerabilities, as the original beta implementation contained insufficient safeguards against malformed data inputs. Network-level protections such as intrusion detection systems can help detect and block suspicious challenge packet patterns, while application-level hardening measures including proper memory management and exception handling should be implemented. Organizations should also consider implementing certificate pinning mechanisms and additional authentication layers to reduce the attack surface and prevent exploitation of this vulnerability. The ATT&CK framework categorizes this as a denial of service attack pattern under the T1499 category, emphasizing the need for both preventive and reactive security measures to protect against such disruptions.