CVE-2026-64452 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
6lowpan: fix NHC entry use-after-free on error path
lowpan_nhc_do_uncompression() looks up an NHC descriptor while holding lowpan_nhc_lock. If the descriptor has no uncompress callback, the error path drops the lock before printing nhc->name.
lowpan_nhc_del() removes descriptors under the same lock and then relies on synchronize_net() before the owning module can be unloaded. That only waits for net RX RCU readers. lowpan_header_decompress() is also exported and can be reached from callers that are not necessarily covered by the net core RX critical section, for example the Bluetooth 6LoWPAN L2CAP receive path.
This leaves a race where one task drops lowpan_nhc_lock in the error path, another task unregisters and frees the matching descriptor after synchronize_net() returns, and the first task then dereferences nhc->name for the warning.
With the post-unlock window widened, KASAN reports:
BUG: KASAN: slab-use-after-free in lowpan_nhc_do_uncompression+0x1f4/0x220 Read of size 8 lowpan_nhc_do_uncompression lowpan_header_decompress
Fix this by printing the warning before dropping lowpan_nhc_lock, so the descriptor name is read while unregister is still excluded. The malformed packet is still rejected with -ENOTSUPP.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability described represents a use-after-free condition in the Linux kernel's 6LoWPAN implementation that arises from improper lock management during error handling paths. This flaw exists within the lowpan_nhc_do_uncompression() function which performs lookup operations on NHC (Next Header Compression) descriptors while holding the lowpan_nhc_lock mutex. The issue occurs when a descriptor lacks an uncompress callback, causing the function to follow an error path that releases the lock before accessing the nhc->name field for diagnostic purposes.
The technical implementation flaw stems from a race condition between concurrent kernel threads executing different code paths that manipulate the same NHC descriptor structure. When lowpan_nhc_do_uncompression() encounters a descriptor without an uncompress callback, it drops the lowpan_nhc_lock before printing warning information about nhc->name. Meanwhile, lowpan_nhc_del() operates under the same lock and performs cleanup operations including synchronization with synchronize_net() that only waits for network receive RCU readers. However, the 6LoWPAN header decompression functionality is exported and accessible from various kernel subsystems such as Bluetooth L2CAP receive paths that may not be covered by the net core RX critical section.
This race condition creates a window where one thread can release the lock while another thread simultaneously unregisters and frees the matching descriptor structure. When the first thread subsequently attempts to dereference nhc->name for warning output, it accesses memory that has already been freed, resulting in a use-after-free error. The kernel's KASAN (Kernel Address Sanitizer) detection system identifies this as a slab-use-after-free condition where the function lowpan_nhc_do_uncompression attempts to read an 8-byte value from freed memory.
The vulnerability aligns with CWE-416: Use After Free and follows patterns commonly associated with race conditions in kernel data structures. From an ATT&CK framework perspective, this represents a privilege escalation vector through kernel memory corruption that could potentially be exploited by malicious actors with kernel-level access or through kernel exploit chains targeting memory safety issues.
The fix implemented addresses the root cause by reordering operations to print warning information before releasing the lowpan_nhc_lock, ensuring that the descriptor name is accessed while the unregister operation is still excluded from concurrent execution. This approach maintains the existing functionality where malformed packets are properly rejected with -ENOTSUPP error code while eliminating the race condition. The solution follows established kernel programming practices for handling lock ordering and synchronization in multi-threaded environments where shared data structures require careful protection against concurrent access patterns that could lead to memory safety violations.