CVE-2009-1935 in FreeBSD
Summary
by MITRE
Integer overflow in the pipe_build_write_buffer function (sys/kern/sys_pipe.c) in the direct write optimization feature in the pipe implementation in FreeBSD 7.1 through 7.2 and 6.3 through 6.4 allows local users to bypass virtual-to-physical address lookups and read sensitive information in memory pages via unspecified vectors.
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Analysis
by VulDB Data Team • 11/11/2018
The vulnerability described in CVE-2009-1935 represents a critical integer overflow flaw within FreeBSD's pipe implementation that fundamentally compromises memory safety and data confidentiality. This issue exists in the pipe_build_write_buffer function located in sys/kern/sys_pipe.c, specifically within the direct write optimization feature that was introduced to improve performance by reducing memory copies during pipe operations. The vulnerability affects FreeBSD versions 6.3 through 6.4 and 7.1 through 7.2, creating a window of exposure where local attackers can exploit this flaw to gain unauthorized access to memory contents. The integer overflow occurs during the calculation of buffer sizes for pipe operations, where an attacker can manipulate input parameters to cause arithmetic overflow that results in incorrect buffer allocation sizes. This flaw directly relates to CWE-190, which identifies integer overflow conditions that can lead to memory corruption and unauthorized data access.
The technical exploitation of this vulnerability leverages the direct write optimization mechanism that bypasses normal virtual-to-physical address translation processes. When a local user triggers the vulnerable code path, the integer overflow causes the pipe subsystem to allocate insufficient buffer space, which then gets filled with data from adjacent memory regions. This allows attackers to read sensitive information from kernel memory pages that should remain protected, effectively bypassing the memory protection mechanisms that normally prevent such unauthorized access. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system, potentially leading to privilege escalation or information disclosure attacks that align with ATT&CK technique T1003.002 for OS Credential Dumping and T1059.001 for Command and Scripting Interpreter. The flaw is particularly insidious because it operates silently, allowing information leakage without obvious system indicators.
The operational impact of CVE-2009-1935 extends beyond simple information disclosure, as it fundamentally undermines the integrity of FreeBSD's memory management system and creates potential pathways for more sophisticated attacks. Local users can exploit this vulnerability to access kernel memory contents that may include cryptographic keys, passwords, session tokens, or other sensitive data that should remain isolated from user-space processes. The vulnerability's exploitation requires local system access but does not require special privileges, making it particularly concerning for multi-user environments where users may have legitimate access to system resources. Organizations running affected FreeBSD versions face significant risk of data breaches and system compromise, as the vulnerability can be combined with other techniques to achieve more extensive exploitation. The memory read capabilities provided by this flaw can be used to gather information about kernel structures, memory layout, and potentially identify additional vulnerabilities within the system that could be leveraged for further compromise. This vulnerability demonstrates the critical importance of proper integer overflow checking in kernel code and highlights the need for comprehensive security testing of system-level optimizations. The impact is particularly severe in environments where FreeBSD systems handle sensitive data or serve as critical infrastructure components, as the vulnerability could enable attackers to extract confidential information that would otherwise be protected by kernel memory management.