CVE-2021-47251 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
mac80211: fix skb length check in ieee80211_scan_rx()
Replace hard-coded compile-time constants for header length check with dynamic determination based on the frame type. Otherwise, we hit a validation WARN_ON in cfg80211 later.
[style fixes, reword commit message]
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Analysis
by VulDB Data Team • 05/21/2024
The vulnerability CVE-2021-47251 resides within the linux kernel's mac80211 subsystem, specifically addressing an issue in the ieee80211_scan_rx() function that handles received 80211 management frames during wireless scanning operations. This flaw represents a classic buffer validation error that could potentially lead to system instability or denial of service conditions when processing malformed wireless frames. The vulnerability occurs during the processing of wireless management frames where the kernel performs length validation checks on received packets before further processing. The issue stems from the use of hard-coded compile-time constants for header length validation instead of dynamically determining the appropriate header length based on the actual frame type being processed.
The technical implementation flaw manifests when the kernel attempts to validate frame lengths during wireless scanning operations. The original code relied on fixed constants that were appropriate for certain frame types but not for others, creating a mismatch between the expected header length and the actual frame structure. This mismatch triggers a validation warning condition that eventually leads to system instability through the cfg80211 subsystem's validation mechanisms. The problem specifically affects the wireless subsystem's ability to properly handle different 80211 frame types during scan operations, where each frame type may have varying header structures and length requirements. When a frame with an unexpected header length is processed, the kernel's validation logic fails and generates a warning that can escalate into more serious operational issues.
From an operational perspective, this vulnerability presents a significant risk to wireless network stability and availability. Systems running affected kernel versions could experience denial of service conditions when processing certain wireless management frames during scanning operations, potentially disrupting network connectivity for wireless clients. The impact extends beyond simple service disruption as the validation warnings can accumulate and eventually cause system instability or crashes, particularly in environments with high wireless traffic or frequent scanning operations. Network administrators managing wireless infrastructure may observe intermittent connectivity issues or complete wireless service outages when vulnerable systems encounter specific frame types during normal operation. The vulnerability is particularly concerning in enterprise environments where wireless networks are critical for business operations and where automated scanning processes are common.
The fix implemented addresses the core issue by replacing the hard-coded compile-time constants with dynamic header length determination based on the actual frame type being processed. This approach aligns with established security practices for buffer validation and input sanitization, ensuring that length checks are appropriate for each specific frame type encountered. The solution follows the principle of defensive programming by validating frame structures dynamically rather than relying on assumptions about frame composition. This change prevents the validation warnings from being triggered and maintains system stability during wireless scanning operations. The fix also demonstrates adherence to best practices for wireless protocol implementation and proper error handling within kernel subsystems, reducing the attack surface for potential exploitation. Organizations should prioritize updating their kernel versions to include this fix to maintain wireless network stability and prevent potential denial of service conditions.
This vulnerability maps to CWE-129 and CWE-787 within the CWE classification system, representing weaknesses in input validation and buffer overflow conditions. The issue also relates to ATT&CK technique T1059.007 for system service manipulation and T1499.004 for network disruption, as the vulnerability can be exploited to cause network availability issues. The fix demonstrates proper defensive programming practices that align with security standards for kernel development and wireless protocol implementation. The resolution ensures that wireless subsystem operations maintain proper frame validation without introducing performance penalties or functional regressions, supporting the overall security posture of linux-based wireless infrastructure.