CVE-2009-2846 in Linux
Summary
by MITRE
The eisa_eeprom_read function in the parisc isa-eeprom component (drivers/parisc/eisa_eeprom.c) in the Linux kernel before 2.6.31-rc6 allows local users to access restricted memory via a negative ppos argument, which bypasses a check that assumes that ppos is positive and causes an out-of-bounds read in the readb function.
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability described in CVE-2009-2846 resides within the Linux kernel's parisc architecture support, specifically in the eisa_eeprom_read function located in drivers/parisc/eisa_eeprom.c. This flaw represents a classic case of improper input validation that enables privilege escalation through memory access bypass. The issue affects kernel versions prior to 2.6.31-rc6 and demonstrates how seemingly minor validation logic can create significant security implications in kernel space operations.
The technical root cause of this vulnerability stems from a flawed assumption within the kernel code that the ppos parameter, which represents the position within the EEPROM data structure, will always be a positive value. When a negative ppos argument is passed to the eisa_eeprom_read function, the existing validation logic fails to properly handle this edge case, allowing malicious local users to manipulate the function's behavior. This bypass occurs because the check that validates ppos assumes positive values and does not account for negative inputs that could potentially point to memory locations outside the intended EEPROM data boundaries.
The operational impact of this vulnerability is particularly concerning as it enables local users to perform out-of-bounds memory reads through the readb function, which is typically used for reading single byte values from memory locations. This capability allows attackers to access restricted memory regions that should normally be protected from direct user-space access. The vulnerability essentially creates a pathway for information disclosure where attackers can read kernel memory contents, potentially exposing sensitive data including cryptographic keys, credentials, or other confidential information stored in kernel memory spaces.
This vulnerability maps to CWE-129 Improper Validation of Array Indices, which specifically addresses issues where array or buffer indices are not properly validated, leading to out-of-bounds access. The flaw also aligns with ATT&CK technique T1068 Exploitation for Privilege Escalation, as local users can leverage this vulnerability to gain elevated privileges by accessing kernel memory regions that contain sensitive information. Additionally, the vulnerability demonstrates characteristics of T1547.001 Account Manipulation, where local users can exploit kernel-level flaws to bypass security controls.
The mitigation for this vulnerability requires implementing proper input validation for the ppos parameter to ensure that negative values are rejected or properly handled within the function. The fix involves adding explicit checks to validate that ppos is within acceptable bounds before proceeding with memory operations, preventing the bypass of the positive value assumption. Kernel updates to version 2.6.31-rc6 or later resolve this issue by implementing proper validation logic that prevents negative ppos values from causing out-of-bounds memory access. Organizations should prioritize applying these kernel updates and monitoring for any potential exploitation attempts that might attempt to leverage this memory access vulnerability for information gathering or privilege escalation activities.