CVE-2017-16927 in xrdp
Summary
by MITRE
The scp_v0s_accept function in sesman/libscp/libscp_v0.c in the session manager in xrdp through 0.9.4 uses an untrusted integer as a write length, which allows local users to cause a denial of service (buffer overflow and application crash) or possibly have unspecified other impact via a crafted input stream.
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Analysis
by VulDB Data Team • 01/16/2023
The vulnerability identified as CVE-2017-16927 resides within the xrdp session management component, specifically in the sesman/libscp/libscp_v0.c file where the scp_v0s_accept function processes incoming data streams. This flaw represents a classic buffer overflow condition that occurs when untrusted integer values are used as write lengths during data processing operations. The issue affects xrdp versions through 0.9.4, making it a significant concern for organizations relying on this remote desktop protocol implementation for secure access to their systems.
The technical root cause of this vulnerability stems from improper input validation and sanitization within the session management layer of xrdp. When the scp_v0s_accept function processes incoming data, it accepts an integer value that should represent the length of data to be written to a buffer but fails to validate whether this integer value is within acceptable bounds. This unvalidated integer can be manipulated by local attackers to exceed the allocated buffer size, leading to memory corruption that manifests as application crashes or potential arbitrary code execution. The vulnerability is classified as a buffer overflow under CWE-121 and represents a specific instance of CWE-787, where an out-of-bounds write occurs due to insufficient bounds checking.
The operational impact of CVE-2017-16927 extends beyond simple denial of service conditions, as local users with access to the system can exploit this vulnerability to cause system instability and potentially gain elevated privileges. When exploited, the buffer overflow can lead to application crashes that disrupt legitimate user sessions, creating a denial of service condition that affects authorized users attempting to establish remote connections. The unspecified other impacts mentioned in the CVE description suggest that under certain conditions, this vulnerability could potentially allow for privilege escalation or information disclosure, making it a particularly dangerous flaw in environments where xrdp is used for remote administration. Attackers could leverage this vulnerability through the ATT&CK technique of privilege escalation by exploiting weaknesses in system components that handle authentication and session management.
Mitigation strategies for CVE-2017-16927 should prioritize immediate patching of xrdp installations to versions beyond 0.9.4 where the vulnerability has been addressed. Organizations should implement network segmentation to limit local access to xrdp services and employ monitoring solutions to detect unusual patterns in session management operations. Additionally, system administrators should conduct regular security assessments of remote desktop implementations and ensure that proper access controls are in place to minimize the attack surface. The vulnerability highlights the importance of input validation and bounds checking in security-critical components, particularly those handling user-provided data streams in session management systems.