CVE-2018-8789 in FreeRDP
Summary
by MITRE
FreeRDP prior to version 2.0.0-rc4 contains several Out-Of-Bounds Reads in the NTLM Authentication module that results in a Denial of Service (segfault).
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-8789 affects FreeRDP versions prior to 2.0.0-rc4 and specifically targets the NTLM Authentication module within the remote desktop protocol implementation. This issue manifests as multiple out-of-bounds read conditions that occur during the processing of authentication tokens and credential handling within the NTLM authentication framework. The flaw exists in the way the software handles memory access patterns when parsing NTLM authentication messages, particularly during the negotiation phase of the authentication process. These out-of-bounds reads represent a critical security weakness that can be exploited by remote attackers to disrupt service availability.
The technical implementation of this vulnerability stems from inadequate bounds checking within the NTLM authentication module's parsing functions. When FreeRDP receives malformed NTLM authentication data, the software fails to properly validate array indices and buffer boundaries before accessing memory locations. This programming error falls under the CWE-129 weakness category, which specifically addresses insufficient bounds checking in array access operations. The vulnerability is particularly dangerous because it occurs during the authentication handshake process, meaning that an attacker could potentially exploit this flaw before establishing a legitimate session, making it a prime target for denial of service attacks.
From an operational impact perspective, this vulnerability directly enables a denial of service condition that results in segmentation faults and application crashes within the FreeRDP implementation. When exploited, the out-of-bounds reads cause the software to access memory locations outside the intended buffer boundaries, leading to unpredictable behavior and ultimately system termination. This type of vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting remote desktop services. The impact extends beyond simple service disruption as it can affect enterprise environments where FreeRDP is used for remote administration, potentially compromising business continuity and system availability for legitimate users.
The exploitation of CVE-2018-8789 requires an attacker to send specially crafted NTLM authentication messages to a vulnerable FreeRDP server instance. The attack vector is remote and does not require authentication, making it particularly dangerous in network environments where FreeRDP services are exposed to untrusted networks. Security researchers have noted that the vulnerability affects both client and server implementations of FreeRDP, meaning that either component could be targeted to cause service disruption. Organizations using FreeRDP for remote desktop connections should consider this vulnerability as a critical threat to their remote access infrastructure, particularly in environments where service availability is paramount.
Mitigation strategies for this vulnerability center around immediate software updates to FreeRDP version 2.0.0-rc4 or later, which contains the necessary patches to address the out-of-bounds read conditions. System administrators should also implement network segmentation and access controls to limit exposure of FreeRDP services to untrusted networks. Additional defensive measures include monitoring for unusual authentication patterns and implementing intrusion detection systems that can identify potential exploitation attempts. The vulnerability demonstrates the importance of proper input validation and bounds checking in security-critical applications, particularly those handling authentication protocols that are frequently targeted by attackers seeking to disrupt service availability. Organizations should also consider implementing redundant authentication mechanisms and backup access methods to maintain operational continuity in case of service disruption.