CVE-2006-4655 in Solaris
Summary
by MITRE
Buffer overflow in the Strcmp function in the XKEYBOARD extension in X Window System X11R6.4 and earlier, as used in SCO UnixWare 7.1.3 and Sun Solaris 8 through 10, allows local users to gain privileges via a long _XKB_CHARSET environment variable value.
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Analysis
by VulDB Data Team • 02/17/2017
The vulnerability identified as CVE-2006-4655 represents a critical buffer overflow condition within the X Window System's X11R6.4 implementation, specifically affecting the Strcmp function within the XKEYBOARD extension. This flaw exists in multiple operating systems including SCO UnixWare 7.1.3 and Sun Solaris versions 8 through 10, creating a widespread security risk across Unix-based systems. The vulnerability stems from inadequate input validation mechanisms that fail to properly handle excessively long string inputs, particularly when processing the _XKB_CHARSET environment variable.
The technical implementation of this vulnerability involves the Strcmp function within the XKEYBOARD extension receiving an unbounded input through the _XKB_CHARSET environment variable. When this variable contains a string exceeding the allocated buffer size, the function fails to perform proper bounds checking, resulting in memory corruption that can be exploited to overwrite adjacent memory locations. This buffer overflow condition occurs because the X Window System does not implement proper input sanitization for environment variables that are processed during X11 extension initialization. The flaw specifically affects the XKEYBOARD extension which handles keyboard input processing and character set definitions, making it particularly dangerous as it operates within the graphical environment where privilege escalation opportunities exist.
The operational impact of this vulnerability is significant as local users can leverage this buffer overflow to achieve privilege escalation within the X Window System environment. The attack vector requires only local system access, making it particularly concerning for multi-user systems where untrusted users might attempt to exploit this condition. When successfully exploited, the buffer overflow can allow attackers to overwrite critical memory structures including return addresses or function pointers, potentially enabling arbitrary code execution with elevated privileges. This vulnerability directly relates to CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios, both of which are fundamental categories in the Common Weakness Enumeration taxonomy that define the underlying nature of the memory corruption issue.
The exploitation of this vulnerability aligns with several techniques documented in the MITRE ATT&CK framework, particularly under the privilege escalation and defense evasion categories. Attackers can utilize this condition to bypass security controls that rely on proper input validation and memory management within the X Window System. The vulnerability's impact extends beyond simple local privilege escalation as it affects the fundamental security model of graphical environments, potentially allowing attackers to compromise user sessions and access protected resources. System administrators should note that this vulnerability affects widely deployed operating systems and requires immediate attention to prevent exploitation by malicious users within the local environment.
Mitigation strategies for CVE-2006-4655 should include immediate patching of affected X Window System implementations, particularly versions prior to X11R6.5 which contain the necessary fixes for buffer overflow conditions in the XKEYBOARD extension. System administrators should also consider implementing environment variable restrictions to limit the size and content of _XKB_CHARSET values that can be processed by X11 applications. Additional protective measures include implementing proper input validation at the application level, utilizing address space layout randomization where available, and monitoring for unusual environment variable usage patterns that might indicate exploitation attempts. Organizations should also review their X Window System configurations to ensure that unnecessary XKEYBOARD extension functionality is disabled when not required, reducing the attack surface for this and similar vulnerabilities. The fix implemented in subsequent X11R6.5 releases specifically addresses the buffer overflow by introducing proper bounds checking for environment variable inputs and ensuring that string operations within the Strcmp function maintain memory integrity during processing.