CVE-2018-7755 in Linux
Summary
by MITRE
An issue was discovered in the fd_locked_ioctl function in drivers/block/floppy.c in the Linux kernel through 4.15.7. The floppy driver will copy a kernel pointer to user memory in response to the FDGETPRM ioctl. An attacker can send the FDGETPRM ioctl and use the obtained kernel pointer to discover the location of kernel code and data and bypass kernel security protections such as KASLR.
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Analysis
by VulDB Data Team • 02/17/2023
The vulnerability identified as CVE-2018-7755 represents a critical information disclosure flaw within the Linux kernel's floppy disk driver implementation. This issue resides in the fd_locked_ioctl function located in drivers/block/floppy.c and affects kernel versions through 4.15.7. The flaw manifests when the FDGETPRM ioctl command is executed, causing the driver to inadvertently copy kernel pointers into user-accessible memory regions. This represents a fundamental breakdown in kernel memory protection mechanisms that directly undermines the security architecture designed to isolate user-space processes from kernel-space operations.
The technical exploitation of this vulnerability stems from the improper handling of kernel pointers within the ioctl interface. When an attacker issues the FDGETPRM command, the floppy driver copies a kernel pointer value to user memory without proper sanitization or access control measures. This pointer typically contains the virtual address of kernel code or data structures, which can be read by any user-space process with access to the floppy device. The vulnerability specifically targets the KASLR (Kernel Address Space Layout Randomization) protection mechanism, which is designed to randomize kernel memory layout to prevent attackers from easily determining kernel addresses. By obtaining these kernel pointers, attackers can effectively bypass KASLR protections and gain valuable information about kernel memory layout.
The operational impact of this vulnerability extends beyond simple information disclosure, creating a foundation for more sophisticated attacks. An attacker who successfully exploits this vulnerability can map kernel memory addresses, potentially enabling them to perform kernel code execution attacks or escalate privileges. The exposure of kernel pointers provides attackers with critical information needed for bypassing various kernel security features, including SMEP (Supervisor Mode Execution Prevention) and SMAP (Supervisor Mode Access Prevention). This vulnerability aligns with CWE-200 (Information Exposure) and represents a classic example of how improper input validation and memory handling can lead to privilege escalation. The ATT&CK framework categorizes this as a technique for privilege escalation through kernel exploitation, specifically targeting the kernel's memory management subsystem.
Mitigation strategies for CVE-2018-7755 primarily involve kernel updates and system hardening measures. The most effective solution is to upgrade to a kernel version that contains the fix for this vulnerability, which was addressed in kernel versions beyond 4.15.7. System administrators should also implement device access controls to restrict access to floppy devices, particularly in production environments where such hardware is not required. Additional mitigations include disabling the floppy driver entirely through kernel configuration options or using module blacklisting to prevent loading of the vulnerable driver. Network-based protections should focus on monitoring for suspicious ioctl operations targeting the floppy device, while endpoint protection solutions can be configured to alert on unusual kernel pointer access patterns. Organizations should also consider implementing runtime protection measures that monitor for unauthorized kernel memory access attempts and maintain comprehensive logging of device ioctl operations for forensic analysis purposes.