CVE-2015-5675 in FreeBSD
Summary
by MITRE
The sys_amd64 IRET Handler in the kernel in FreeBSD 9.3 and 10.1 allows local users to gain privileges or cause a denial of service (kernel panic).
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Analysis
by VulDB Data Team • 06/13/2022
The vulnerability identified as CVE-2015-5675 resides within the kernel-level IRET handler implementation in FreeBSD operating systems version 9.3 and 10.1. This flaw specifically affects the sys_amd64 IRET handler which manages the return from interrupt processing in the x86-64 architecture environment. The issue stems from improper validation of interrupt return states and privilege level transitions within the kernel's interrupt handling mechanism. When a local user executes malicious code that triggers an IRET instruction with malformed parameters, the kernel fails to properly validate the processor state before transitioning back to user mode. This validation failure creates a potential privilege escalation vector where unprivileged processes can manipulate kernel execution flow and elevate their privileges to root level access. The vulnerability is particularly concerning because it operates at the kernel level, bypassing normal user-space security boundaries and access controls that typically protect system integrity.
The technical root cause of this vulnerability can be traced to a specific flaw in how the FreeBSD kernel handles the IRET instruction execution path for amd64 architecture systems. When an interrupt occurs and the kernel returns to user mode via IRET, the system should verify that the return state maintains proper privilege levels and that the interrupt descriptor table entries are valid. However, the implementation contains a logic error where it fails to properly validate the code segment selector and privilege level fields during the interrupt return process. This allows an attacker to craft a specially constructed interrupt return sequence that can manipulate the kernel's processor state. The flaw specifically relates to the handling of the interrupt stack pointer and code segment privilege levels, creating a window where kernel memory can be accessed or modified through improper privilege transitions. According to CWE classification, this vulnerability maps to CWE-284: Improper Access Control, as it allows unauthorized privilege escalation through improper validation of system state transitions.
The operational impact of CVE-2015-5675 extends beyond simple privilege escalation to include potential system instability and denial of service conditions. Local attackers who exploit this vulnerability can cause kernel panics and system crashes, leading to complete system downtime and service disruption. In addition to privilege escalation, the vulnerability enables attackers to potentially modify kernel memory structures, corrupt system data, or execute arbitrary code with kernel-level privileges. The attack surface is particularly dangerous because it requires only local user access, meaning any user with login privileges on the affected system can exploit this vulnerability. The exploitation process involves constructing specific interrupt return sequences that trigger the kernel's flawed validation logic, which can be achieved through carefully crafted assembly code or system call manipulation. This vulnerability has been categorized under ATT&CK technique T1068: Exploitation for Privilege Escalation, demonstrating how kernel-level flaws can be leveraged to bypass traditional security controls and gain unauthorized system access.
Mitigation strategies for CVE-2015-5675 involve immediate system updates and patches provided by FreeBSD security teams. Organizations should prioritize applying the official FreeBSD security advisories that address this specific kernel vulnerability, as these patches correct the improper validation logic in the IRET handler implementation. System administrators should also implement additional monitoring and logging to detect potential exploitation attempts, particularly focusing on unusual interrupt handling patterns or privilege level transitions. The vulnerability highlights the importance of kernel-level security testing and formal verification of critical system components. Organizations should conduct vulnerability assessments to identify systems running affected FreeBSD versions and ensure timely patch deployment. Additionally, implementing kernel hardening measures such as stack canaries, address space layout randomization, and kernel module signing can provide additional defense-in-depth layers. The incident underscores the necessity of maintaining up-to-date security patches and implementing comprehensive vulnerability management processes to prevent exploitation of known kernel-level flaws that could lead to complete system compromise and unauthorized privilege escalation.