CVE-2018-5995 in Linux
Summary
by MITRE
The pcpu_embed_first_chunk function in mm/percpu.c in the Linux kernel through 4.14.14 allows local users to obtain sensitive address information by reading dmesg data from a "pages/cpu" printk call.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/01/2023
The vulnerability identified as CVE-2018-5995 resides within the Linux kernel's per-CPU memory management subsystem, specifically in the pcpu_embed_first_chunk function located in mm/percpu.c. This flaw represents a information disclosure vulnerability that affects Linux kernel versions through 4.14.14, creating a significant security risk for systems running these kernel versions. The vulnerability manifests through a seemingly innocuous printk call that outputs memory layout information to the kernel's dmesg buffer, which can be accessed by local unprivileged users.
The technical implementation of this vulnerability exploits the kernel's per-CPU memory allocation mechanism where the pcpu_embed_first_chunk function is responsible for embedding the first memory chunk of per-CPU data structures. During the initialization process, this function makes a printk call that outputs sensitive address information related to the memory layout of the kernel's per-CPU areas. The dmesg buffer, which is accessible to local users through the /dev/kmsg interface or standard dmesg command, contains this address information that reveals kernel memory layout details. This addressespace disclosure occurs because the function does not properly sanitize the memory addresses before outputting them to the kernel log, creating a predictable pattern that adversaries can exploit for further attacks.
From an operational perspective, this vulnerability allows local attackers to gain knowledge of kernel memory addresses that can be leveraged for privilege escalation attempts or other advanced exploitation techniques. The information disclosed through dmesg can be used to bypass kernel address space layout randomization (ASLR) protections, which are fundamental security mechanisms designed to make exploitation of memory corruption vulnerabilities more difficult. Attackers can use this information to craft more effective exploits against other vulnerabilities present in the kernel or to perform advanced attack techniques such as return-oriented programming (ROP) or jump-oriented programming (JOP) that require knowledge of memory layout. The vulnerability is particularly concerning because it requires no special privileges to exploit and can be triggered by any local user with access to the system.
The security implications extend beyond simple information disclosure, as this vulnerability aligns with several attack patterns documented in the ATT&CK framework under techniques such as privilege escalation and defense evasion. The CWE (Common Weakness Enumeration) classification for this vulnerability would be CWE-200, Information Exposure, specifically related to the improper disclosure of information through kernel logs. This weakness can be classified as CWE-312, Cleartext Storage of Sensitive Information, as the memory addresses are stored and exposed in clear text within the kernel's dmesg buffer. The vulnerability demonstrates poor input validation and output sanitization practices in kernel code, where sensitive information is inadvertently exposed through kernel logging mechanisms. System administrators and security professionals should consider this vulnerability as part of a broader security posture assessment, particularly in environments where local user access cannot be fully trusted. The recommended mitigations include updating to kernel versions that have patched this vulnerability, implementing proper access controls to limit dmesg access, and monitoring for suspicious dmesg entries that might indicate exploitation attempts. Additionally, organizations should consider implementing kernel hardening techniques such as disabling unnecessary kernel logging or implementing custom kernel configurations that prevent such information disclosure vulnerabilities from occurring in the first place.