CVE-2021-42008 in Linux
Summary
by MITRE • 10/05/2021
The decode_data function in drivers/net/hamradio/6pack.c in the Linux kernel before 5.13.13 has a slab out-of-bounds write. Input from a process that has the CAP_NET_ADMIN capability can lead to root access.
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Analysis
by VulDB Data Team • 06/21/2025
The vulnerability identified as CVE-2021-42008 represents a critical security flaw in the Linux kernel's hamradio subsystem, specifically within the 6pack.c driver file. This issue affects kernel versions prior to 5.13.13 and demonstrates a classic slab out-of-bounds write vulnerability that can be exploited to gain elevated privileges. The vulnerability resides in the decode_data function which processes input data from network communication protocols used in amateur radio applications. The flaw allows for memory corruption that can be leveraged by malicious actors to execute arbitrary code with kernel-level privileges.
The technical nature of this vulnerability stems from improper bounds checking within the decode_data function, which fails to validate the size of input data before writing to kernel memory buffers. This slab out-of-bounds write condition occurs when the function processes data from processes possessing the CAP_NET_ADMIN capability, a network administration privilege typically required for configuring network interfaces and managing network protocols. The vulnerability creates an opportunity for attackers to overwrite adjacent memory locations in the kernel's slab allocator, potentially allowing them to manipulate kernel data structures or inject malicious code into the kernel space.
The operational impact of CVE-2021-42008 is severe given that exploitation requires only a process with CAP_NET_ADMIN capability, which can be obtained through various legitimate means such as network administration tasks or specific user permissions. Once exploited, the vulnerability provides attackers with root access to the affected system, enabling complete compromise of the kernel and all running processes. This privilege escalation allows adversaries to bypass traditional security controls, access sensitive data, modify system configurations, and establish persistent backdoors. The vulnerability affects systems running Linux kernel versions earlier than 5.13.13, making it particularly concerning for organizations maintaining older kernel versions or those with delayed patching cycles.
Security professionals should note that this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1068, which involves exploiting legitimate credentials or capabilities to escalate privileges. The flaw represents a classic example of how kernel-level vulnerabilities can be exploited through seemingly benign administrative capabilities. Organizations should prioritize patching their systems to kernel version 5.13.13 or later, implementing proper capability management to limit the scope of processes with CAP_NET_ADMIN privileges, and monitoring for unusual network activity that might indicate exploitation attempts. The vulnerability underscores the importance of kernel security hardening and maintaining up-to-date system configurations to prevent exploitation of similar memory corruption vulnerabilities.