CVE-2018-20179 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Integer Underflow that leads to a Heap-Based Buffer Overflow in the function lspci_process() and results in memory corruption and probably even a remote code execution.
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2018-20179 represents a critical security flaw in rdesktop versions up to and including v1.8.3 that stems from an integer underflow condition within the lspci_process() function. This issue falls under the Common Weakness Enumeration category CWE-190, which specifically addresses integer overflow and underflow conditions that can lead to memory corruption vulnerabilities. The flaw manifests when processing certain PCI configuration data during remote desktop protocol connections, creating a scenario where an attacker can manipulate input parameters to trigger unexpected behavior in the memory management system.
The technical implementation of this vulnerability involves an integer underflow occurring in the lspci_process() function where unsigned integer arithmetic fails to properly validate input values. When the system processes PCI device information, particularly in scenarios involving malformed or crafted data, the underflow condition causes a negative value to be used as a buffer size parameter. This negative value then gets interpreted as a very large positive integer due to unsigned integer wraparound behavior, leading to heap-based buffer overflow conditions. The memory corruption resulting from this overflow can overwrite adjacent memory regions, potentially corrupting critical program data structures or execution pointers.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable remote code execution within the context of the rdesktop process. Attackers exploiting this flaw can craft malicious PCI configuration data that, when processed by the vulnerable rdesktop client, triggers the integer underflow and subsequent buffer overflow. This allows for arbitrary code execution on the target system, making it particularly dangerous for remote desktop environments where untrusted connections are common. The vulnerability affects the core functionality of rdesktop's PCI device enumeration feature, which is typically used to discover and report hardware configuration details during remote desktop sessions.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1059.007 for remote code execution through protocol manipulation and T1210 for exploitation of remote desktop services. The attack vector typically involves establishing a remote desktop connection to a vulnerable system and then sending specially crafted PCI data that triggers the integer underflow condition. Organizations using rdesktop for remote access should consider this vulnerability as a high-priority threat due to its potential for remote code execution and the widespread use of remote desktop protocols in enterprise environments. The flaw demonstrates how seemingly benign configuration processing functions can become attack surfaces when proper input validation and integer overflow protections are absent.
Mitigation strategies for CVE-2018-20179 include immediate patching of rdesktop installations to versions that have addressed the integer underflow condition through proper input validation and signed integer arithmetic checks. System administrators should implement network segmentation and access controls to limit exposure of rdesktop services to untrusted networks. Additional protective measures include monitoring network traffic for unusual PCI configuration data patterns and implementing intrusion detection systems that can identify potential exploitation attempts. Organizations should also consider disabling unnecessary PCI enumeration features when they are not required for remote desktop operations, reducing the attack surface for this particular vulnerability. The fix typically involves adding proper boundary checks and unsigned integer overflow detection mechanisms within the lspci_process() function to prevent the underflow condition from occurring in the first place.