CVE-2009-2847 in Linux
Summary
by MITRE
The do_sigaltstack function in kernel/signal.c in Linux kernel 2.4 through 2.4.37 and 2.6 before 2.6.31-rc5, when running on 64-bit systems, does not clear certain padding bytes from a structure, which allows local users to obtain sensitive information from the kernel stack via the sigaltstack function.
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Analysis
by VulDB Data Team • 02/04/2025
The vulnerability described in CVE-2009-2847 represents a classic information disclosure issue affecting the Linux kernel's signal handling mechanism. This flaw exists in the do_sigaltstack function within kernel/signal.c and impacts kernel versions from 2.4 through 2.4.37 and all 2.6 versions prior to 2.6.31-rc5 when operating on 64-bit architectures. The vulnerability stems from insufficient memory management during signal stack operations, creating a scenario where sensitive data from kernel memory may be inadvertently exposed to user-space processes.
The technical implementation of this vulnerability involves the improper handling of structure padding bytes during the sigaltstack system call execution. When a process invokes sigaltstack to manipulate signal delivery stacks, the kernel's do_sigaltstack function fails to properly clear padding bytes within the signal stack structure. These padding bytes, which are typically unused portions of memory allocated for alignment purposes, may retain data from previous kernel operations or contain sensitive information from kernel stack memory. On 64-bit systems where memory alignment requirements are more stringent, this issue becomes particularly pronounced as the structure layout and padding requirements differ significantly from 32-bit implementations.
The operational impact of this vulnerability allows local attackers to potentially extract sensitive information from kernel memory through carefully crafted sigaltstack system calls. This information disclosure can include kernel stack contents, memory addresses, or other confidential data that may aid in further exploitation attempts. The vulnerability is classified as a local privilege escalation vector since it requires local access but can potentially provide attackers with kernel memory insights that could be leveraged for more sophisticated attacks. According to CWE-200, this represents an information exposure vulnerability where the system inadvertently reveals information that should remain confidential.
The attack surface for this vulnerability is primarily limited to local users on affected systems, but the implications extend beyond simple information disclosure. An attacker with local access could potentially use this information to bypass security mechanisms, perform kernel address space layout randomization (ASLR) attacks, or gather intelligence for more complex exploitation techniques. The vulnerability aligns with ATT&CK technique T1059.003 for executing commands through the kernel, as it provides a means for extracting kernel-level information that could be used to craft more effective attacks against the system.
Mitigation strategies for this vulnerability include applying the appropriate kernel security patches released by the Linux kernel development team, specifically upgrading to kernel versions 2.6.31-rc5 or later. System administrators should also implement proper access controls to limit local user privileges where possible, as this vulnerability requires local execution to exploit. Additionally, monitoring for unusual sigaltstack system call patterns and implementing kernel memory protection mechanisms can help detect potential exploitation attempts. The fix implemented by the kernel developers typically involves ensuring proper initialization and clearing of structure padding bytes during signal stack operations, preventing the leakage of kernel memory contents to user-space processes.