CVE-2018-8792 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Out-Of-Bounds Read in function cssp_read_tsrequest() that results in a Denial of Service (segfault).
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Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2018-8792 affects rdesktop versions up to and including v1.8.3, presenting a critical out-of-bounds read condition within the cssp_read_tsrequest() function. This flaw manifests as a denial of service condition that typically results in segmentation faults, effectively crashing the affected application. The vulnerability stems from insufficient input validation and boundary checking within the remote desktop protocol implementation, specifically in how the application processes certain TLS handshake messages. When a maliciously crafted TLS request is received during the connection establishment phase, the application fails to properly validate the length of incoming data before attempting to read from memory locations beyond the allocated buffer boundaries.
The technical exploitation of this vulnerability requires an attacker to establish a connection to a vulnerable rdesktop instance and send a specially crafted TLS request that triggers the out-of-bounds memory access. This condition falls under CWE-129, which represents "Improper Validation of Array Index," and specifically relates to improper bounds checking in memory operations. The vulnerability directly impacts the availability of the rdesktop service, as the segmentation fault causes the application to terminate unexpectedly, preventing legitimate users from establishing remote desktop connections. The flaw demonstrates a classic buffer over-read scenario where the application attempts to access memory locations that were not properly validated against the actual data length, leading to unpredictable behavior and system instability.
From an operational perspective, this vulnerability poses significant risks to organizations relying on rdesktop for remote access capabilities, particularly in environments where continuous availability is critical. The denial of service condition can be exploited by remote attackers without authentication, making it particularly dangerous in exposed network environments. The vulnerability aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service," and represents a common attack vector in remote desktop protocol exploitation campaigns. Organizations utilizing rdesktop for remote administration, system maintenance, or employee access may experience service disruptions that could impact business continuity and operational efficiency.
Mitigation strategies for CVE-2018-8792 primarily involve upgrading to rdesktop versions that contain the fix, specifically versions beyond v1.8.3 where the input validation has been strengthened. Network administrators should implement immediate patch management procedures to ensure all affected systems are updated promptly. Additionally, implementing network segmentation and access controls can help reduce the attack surface by limiting exposure of rdesktop services to untrusted networks. Monitoring for unusual connection patterns or failed connection attempts may help detect exploitation attempts, while disabling unnecessary rdesktop services can minimize potential impact. The fix typically involves implementing proper bounds checking and input validation mechanisms within the cssp_read_tsrequest() function to ensure that all memory accesses are validated against the actual data length before processing, thereby preventing the out-of-bounds read condition that leads to the segmentation fault.