CVE-2026-63991 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: 6lowpan: check skb_clone() return value in send_mcast_pkt()
The skb_clone() function can return NULL if memory allocation fails. send_mcast_pkt() calls skb_clone() without checking the return value, which can lead to a NULL pointer dereference in send_pkt() when it dereferences skb->data. Add a NULL check after skb_clone() and skip the peer if the clone fails.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability resides within the linux kernel's bluetooth 6lowpan implementation where a critical null pointer dereference can occur due to inadequate error handling during packet transmission. The flaw specifically manifests in the send_mcast_pkt() function which invokes skb_clone() without validating whether the memory allocation operation succeeds. When memory pressure occurs or allocation fails, skb_clone() returns NULL instead of a valid sk_buff structure pointer, creating a dangerous condition that can lead to system crashes and potential denial of service scenarios.
The technical mechanism behind this vulnerability involves the kernel's network stack processing where the send_mcast_pkt() function attempts to duplicate a socket buffer for multicast transmission. The skb_clone() operation is designed to create a copy of the original sk_buff structure, but when memory allocation fails, it returns NULL without throwing an exception or signal. This NULL return value propagates through the call chain directly to send_pkt() which assumes the pointer is valid and proceeds to dereference skb->data without proper validation, resulting in immediate system termination upon memory access violation.
The operational impact of this vulnerability extends beyond simple system instability as it can be exploited by malicious actors to induce denial of service conditions within bluetooth 6lowpan networks. Attackers could potentially trigger memory allocation failures through resource exhaustion attacks or carefully crafted packet sequences that force the kernel into a state where it cannot allocate sufficient memory for skb_clone() operations. This creates a reliable crash vector that could disrupt network connectivity for legitimate users and compromise system availability in embedded devices or IoT deployments that heavily rely on bluetooth 6lowpan functionality.
From a cybersecurity perspective, this vulnerability aligns with CWE-476 which identifies null pointer dereference as a critical weakness in software systems. The flaw represents a classic defensive programming error where proper error handling mechanisms are absent from memory allocation sequences, violating fundamental security principles of input validation and error state management. This vulnerability also maps to ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion or system crashes, as the null pointer dereference can be reliably triggered to crash kernel processes.
Mitigation strategies should focus on implementing proper NULL checking immediately after skb_clone() calls and establishing graceful failure handling for multicast packet transmission scenarios. The fix involves adding explicit validation checks to verify that the cloned sk_buff structure is valid before proceeding with packet processing, while also implementing appropriate logging mechanisms to track allocation failures and memory pressure conditions. Additionally, system administrators should monitor kernel memory usage patterns and consider implementing resource limits or memory pressure handling policies that prevent allocation failures from occurring in production environments where bluetooth 6lowpan functionality is actively utilized.