CVE-2021-47620 in Linux
Summary
by MITRE • 06/20/2024
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: refactor malicious adv data check
Check for out-of-bound read was being performed at the end of while num_reports loop, and would fill journal with false positives. Added check to beginning of loop processing so that it doesn't get checked after ptr has been advanced.
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Analysis
by VulDB Data Team • 10/04/2025
The vulnerability identified as CVE-2021-47620 represents a critical flaw in the Linux kernel's Bluetooth subsystem that could potentially enable attackers to exploit out-of-bounds memory access patterns. This issue specifically affects how the kernel processes Bluetooth advertising data, which forms the foundation of wireless device discovery and communication in Bluetooth networks. The flaw manifests in the way the kernel handles malformed advertising data packets, creating conditions where memory corruption could occur during the parsing of Bluetooth device information.
The technical implementation of this vulnerability stems from improper boundary checking within the Bluetooth advertising data processing loop. The original code structure placed the out-of-bounds read validation at the conclusion of a while loop that iterates through reported Bluetooth advertisements. This positioning created a scenario where the validation occurred after pointer advancement, leading to false positive detections in system logs and potentially allowing malicious actors to craft advertising packets that could trigger memory access violations. The flaw aligns with CWE-129, which addresses insufficient bound checking, and specifically demonstrates improper input validation in wireless communication protocols.
Operationally, this vulnerability could enable attackers to disrupt Bluetooth services on Linux systems through crafted advertising data packets that cause kernel memory corruption. The false positive journal entries generated by the flawed validation mechanism could also obscure legitimate security events, making it harder for system administrators to detect actual threats. When exploited, the vulnerability might result in system instability, denial of service conditions, or potentially privilege escalation depending on the kernel version and system configuration. The impact extends beyond simple service disruption as it affects the fundamental reliability of Bluetooth communication infrastructure in Linux environments.
The resolution for CVE-2021-47620 involves refactoring the Bluetooth advertising data validation logic by moving the out-of-bounds check to the beginning of the processing loop rather than at its conclusion. This modification ensures that pointer validation occurs before any advancement of the data pointer, preventing the conditions that led to false positives and memory access violations. The fix aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as it addresses a kernel-level vulnerability that could be exploited through crafted network traffic. System administrators should prioritize applying this patch across all Linux systems running Bluetooth services, particularly those in enterprise environments where wireless device management is critical. The mitigation strategy also includes monitoring system logs for unusual patterns in Bluetooth-related journal entries and implementing network segmentation to limit exposure to potentially malicious Bluetooth devices.