CVE-2005-4783 in NetBSD
Summary
by MITRE
kernfs_xread in kernfs_vnops.c in NetBSD before 20050831 does not check for a negative offset when reading the message buffer, which allows local users to read arbitrary kernel memory.
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Analysis
by VulDB Data Team • 07/16/2018
The vulnerability described in CVE-2005-4783 resides within the kernfs filesystem implementation in NetBSD operating systems prior to the 20050831 release. This flaw exists in the kernfs_xread function located in the kernfs_vnops.c source file, which handles read operations on kernel filesystem objects. The issue manifests when the system processes read requests on kernfs nodes without properly validating the offset parameter before accessing kernel memory regions. This represents a classic buffer over-read condition that can be exploited by local malicious users to gain unauthorized access to kernel memory space.
The technical exploitation of this vulnerability stems from the absence of proper input validation within the kernfs_xread function. When a user process attempts to read from a kernfs node, the system fails to verify whether the provided offset value is valid or negative. A negative offset value can cause the kernel to access memory locations that are outside the intended message buffer boundaries, effectively allowing arbitrary memory reads from kernel space. This type of vulnerability falls under the category of improper input validation as defined by CWE-248, where an application fails to properly check the validity of input parameters before processing them. The flaw specifically relates to the lack of bounds checking on offset parameters, creating a path where attackers can manipulate memory access patterns to extract sensitive kernel data.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides local attackers with the ability to read arbitrary kernel memory locations. This capability can be leveraged to extract sensitive information such as kernel pointers, credential data, encryption keys, or other confidential system information that could be used for further exploitation. Attackers might combine this primitive with other vulnerabilities or techniques to escalate privileges or gain deeper system access. The vulnerability affects all NetBSD systems running versions prior to the 20050831 release, making it particularly concerning for systems that have not been updated with the security patch. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as attackers can use this capability to gather system information for reconnaissance purposes, and potentially T1063 for credential access when sensitive kernel data is read.
The mitigation for CVE-2005-4783 involves applying the security patch released by NetBSD on August 31, 2005, which implements proper validation of offset parameters in the kernfs_xread function. System administrators should ensure their NetBSD installations are updated to the patched version or a later release that includes the fix. Additionally, monitoring for unauthorized access attempts or unusual read patterns on kernfs nodes can help detect potential exploitation attempts. The fix typically involves adding a check to ensure that the offset value is non-negative before proceeding with memory access operations, preventing the exploitation of the buffer over-read condition. Organizations should also consider implementing additional security measures such as kernel address space layout randomization and other exploit mitigation techniques to reduce the overall attack surface. This vulnerability demonstrates the critical importance of input validation in kernel code and the potential consequences when such validation is omitted, emphasizing the need for comprehensive security testing of kernel subsystems.