CVE-2017-7523 in cygwin
Summary
by MITRE
Cygwin versions 1.7.2 up to and including 1.8.0 are vulnerable to buffer overflow vulnerability in wcsxfrm/wcsxfrm_l functions resulting into denial-of-service by crashing the process or potential hijack of the process running with administrative privileges triggered by specially crafted input string.
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Analysis
by VulDB Data Team • 10/31/2019
The vulnerability identified as CVE-2017-7523 represents a critical buffer overflow flaw affecting Cygwin versions 1.7.2 through 1.8.0, specifically within the wcsxfrm and wcsxfrm_l functions. This issue stems from improper handling of wide character string transformations where the implementation fails to properly validate input lengths before performing memory operations. The flaw exists in the underlying locale-aware string transformation functions that are commonly used throughout the Cygwin environment for internationalization support. When maliciously crafted wide character input strings are processed through these functions, the insufficient bounds checking leads to memory corruption that can result in arbitrary code execution or system instability.
The technical implementation of this vulnerability occurs in the wcsxfrm family of functions which are designed to transform wide character strings according to locale-specific rules for proper string comparison operations. The buffer overflow manifests when the function attempts to copy or process input strings that exceed predetermined buffer sizes without adequate validation mechanisms. This particular flaw falls under the CWE-121 CWE category for stack-based buffer overflow, though the actual memory corruption may occur in heap-based structures depending on the specific implementation details. The vulnerability is particularly dangerous because it can be triggered by any application or process that utilizes these functions, making it a widespread threat across the Cygwin ecosystem.
From an operational perspective, this vulnerability presents significant risk to systems running affected Cygwin versions, particularly those executing with elevated privileges. The potential for privilege escalation exists when the vulnerable functions are called by processes running with administrative rights, as demonstrated by the possibility of process hijacking. The denial-of-service impact can be severe for critical systems where Cygwin components are integral to operations, potentially causing service interruptions that could affect business continuity. Attackers can exploit this vulnerability by crafting specially formatted wide character strings that when processed through the affected functions trigger the buffer overflow condition, leading to either application crashes or in more sophisticated scenarios, complete system compromise.
The mitigation strategies for CVE-2017-7523 primarily involve immediate patching of affected Cygwin installations to versions that contain fixed implementations of the wcsxfrm functions. System administrators should prioritize updating to Cygwin 1.8.1 or later, which includes proper bounds checking and input validation mechanisms. Additionally, implementing runtime protections such as stack canaries and address space layout randomization can provide defense-in-depth measures against exploitation attempts. Network segmentation and privilege separation practices should be enforced to limit the potential impact if exploitation occurs, ensuring that applications using these functions do not run with unnecessary administrative privileges. The ATT&CK framework categorizes this vulnerability under T1068 for exploit for privilege escalation, highlighting the need for comprehensive security measures beyond simple patching to address the broader attack surface implications.