CVE-2021-34866 in Linux
Summary
by MITRE • 01/25/2022
This vulnerability allows local attackers to escalate privileges on affected installations of Linux Kernel 5.14-rc3. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability. The specific flaw exists within the handling of eBPF programs. The issue results from the lack of proper validation of user-supplied eBPF programs, which can result in a type confusion condition. An attacker can leverage this vulnerability to escalate privileges and execute arbitrary code in the context of the kernel. Was ZDI-CAN-14689.
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Analysis
by VulDB Data Team • 06/10/2026
This vulnerability represents a critical privilege escalation flaw in the Linux kernel version 5.14-rc3 that specifically targets the eBPF (extended Berkeley Packet Filter) subsystem. The vulnerability falls under the category of type confusion issues that arise from inadequate validation of user-supplied data within kernel space operations. The flaw exists within the kernel's eBPF program handling mechanisms where insufficient input validation allows maliciously crafted eBPF programs to trigger unexpected behavior in the kernel's memory management systems. This vulnerability is particularly dangerous because it operates within the kernel context, providing attackers with direct access to privileged execution environments where they can manipulate system resources and potentially gain full administrative control over affected systems.
The technical implementation of this vulnerability stems from improper validation procedures within the eBPF subsystem that processes user-space programs for kernel execution. When eBPF programs are loaded into the kernel, the system should validate program structures and memory layouts to prevent corruption of kernel data structures. However, the flaw allows attackers to craft eBPF programs that can manipulate the kernel's internal type handling mechanisms, causing the kernel to misinterpret data types during program execution. This type confusion condition creates opportunities for memory corruption that can be exploited to overwrite critical kernel data structures or function pointers. The vulnerability is categorized as CWE-121 and CWE-122, representing stack-based buffer overflow conditions and heap-based buffer overflow conditions respectively, with specific implications for kernel memory management systems. The attack vector requires local execution privileges, making this a local privilege escalation vulnerability that can be leveraged by attackers who have already gained access to a low-privileged user account on the target system.
The operational impact of this vulnerability extends beyond simple privilege escalation, as successful exploitation can lead to complete system compromise and persistent access to affected systems. Attackers who exploit this vulnerability can execute arbitrary code with kernel-level privileges, enabling them to modify system files, install backdoors, monitor network traffic, or disable security mechanisms. The eBPF subsystem's legitimate use for network packet filtering, system monitoring, and performance analysis makes this vulnerability particularly dangerous because legitimate eBPF programs are already expected to run on systems, increasing the attack surface without requiring additional system modifications. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1068, which involves exploiting legitimate credentials and privileges to gain system access, and T1059, which involves executing commands through legitimate system processes. The vulnerability's exploitation can bypass many traditional security controls since eBPF programs are typically trusted by the kernel and do not require elevated privileges to load, making this a stealthy and effective attack vector for persistent threats.
Mitigation strategies for this vulnerability should focus on immediate patching of affected kernel versions and implementation of additional security controls to limit eBPF program execution. System administrators should prioritize updating to kernel versions that contain fixes for this vulnerability, as the Linux kernel development team has addressed this issue in subsequent releases. Additional protective measures include implementing strict eBPF program validation policies, monitoring for suspicious eBPF program loading activities, and restricting user access to eBPF functionality where possible. Organizations should also consider implementing kernel module signing requirements and using eBPF program sandboxing techniques to limit the potential impact of malicious eBPF programs. The vulnerability highlights the importance of comprehensive input validation in kernel space operations and demonstrates the critical need for rigorous security testing of system call interfaces that handle user-supplied data. Security monitoring should specifically target eBPF program loading events and anomalous memory access patterns that could indicate exploitation attempts, as these activities may precede privilege escalation or other malicious actions within the system.