CVE-2026-64006 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: fix dst corruption in same register operation
For lshift and rshift, the shift operations are performed in a loop over 32-bit words. The loop calculates the shifted value and write it to dst, and then immediately reads from src to calculate the carry for the next iteration. Because src and dst could point to the same memory location, the carry is incorrectly calculated using the newly modified dst value instead of the original src value.
Adding a temporary local variable to cache the original value before writing to dst and using it for the carry calculation solves the problem. In addition, partial overlap is rejected from control plane for all kind of operations including byteorder. This was tested with the following bytecode:
table test_table ip flags 0 use 1 handle 1 ip test_table test_chain use 3 type filter hook input prio 0 policy accept packets 0 bytes 0 flags 1 ip test_table test_chain 2 [ immediate reg 1 0x44332211 0x88776655 ]
[ bitwise reg 1 = ( reg 1 << 0x08000000 ) ]
[ cmp eq reg 1 0x66443322 0x00887766 ]
[ counter pkts 0 bytes 0 ]
ip test_table test_chain 4 3 [ immediate reg 1 0x44332211 0x88776655 ]
[ bitwise reg 1 = ( reg 1 << 0x08000000 ) ]
[ cmp eq reg 1 0x55443322 0x00887766 ]
[ counter pkts 21794 bytes 1917798 ]
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability exists within the Linux kernel's netfilter subsystem, specifically in the nf_tables component that handles packet filtering and manipulation. This issue affects the bitwise shift operations including left shift lshift and right shift rshift implementations. The flaw occurs when processing shift operations on 32-bit words within a loop structure where the destination register may reference the same memory location as the source register. The problematic behavior stems from how carry calculations are performed during multi-word shift operations, creating a scenario where subsequent iterations use modified destination values instead of original source values for carry computations.
The technical root cause involves a classic memory aliasing problem where src and dst registers can point to identical memory locations, causing the carry calculation logic to reference corrupted data. During the loop execution, each iteration calculates the shifted value and writes it to the destination register before immediately reading from the source register to compute the carry for the next iteration. When the registers overlap, this sequence results in using the already-modified destination values as source inputs for carry calculations, leading to incorrect final outputs. This type of vulnerability falls under CWE-129 Input Validation and OWASP Top Ten category A03: Injection, specifically manifesting as a memory corruption issue that affects data integrity during processing.
The operational impact of this vulnerability is significant for systems running Linux kernels with netfilter functionality, particularly those implementing packet filtering rules with bitwise operations. Attackers could potentially exploit this flaw to manipulate packet filtering decisions by crafting malicious nf_tables bytecode that leverages the register overlap scenario. The vulnerability allows for incorrect shift calculations that could alter packet contents or bypass security controls, making it a critical concern for network security implementations. Systems utilizing complex packet filtering chains with overlapping register operations are particularly at risk.
The fix implemented addresses this issue through two primary mechanisms: first, introducing a temporary local variable to cache the original source value before any modifications are written to the destination register, ensuring carry calculations use pristine data; second, rejecting partial overlaps from the control plane for all operations including byteorder transformations. This dual approach prevents both the immediate memory aliasing issue and prevents the creation of potentially problematic rule configurations. The solution aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, by preventing malicious code injection through flawed data processing pathways, and follows security best practices for avoiding memory corruption vulnerabilities in kernel space operations. Testing confirmed the fix using specific bytecode sequences that previously demonstrated the corruption behavior, with the corrected implementation showing proper shift operation results.