CVE-2026-72350 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: xt_u32: reject invalid shift counts
u32_match_it() executes rule-supplied shift operands on a 32-bit value. A malformed u32 rule can provide a shift count of 32 or more, triggering an undefined shift out-of-bounds during packet evaluation.
Validate XT_U32_LEFTSH and XT_U32_RIGHTSH operands in u32_mt_checkentry() and reject malformed rules before they reach the packet path.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides within the Linux kernel's netfilter framework, specifically in the xt_u32 match module which implements pattern matching for packet headers using 32-bit values. This module processes rule-defined shift operations that manipulate data within packet contents during network filtering. The core issue manifests when maliciously crafted u32 rules contain shift counts of 32 or more bits, which exceed the valid range for 32-bit arithmetic operations.
The technical flaw occurs in the u32_match_it() function where rule-supplied shift operands are executed against 32-bit values without proper validation. When a shift count equals or exceeds 32 bits, it results in undefined behavior due to out-of-bounds shifting operations that can cause unpredictable memory access patterns and potential kernel crashes. This vulnerability falls under the CWE-758 weakness category for unspecified other weakness related to improper handling of shift operations. The flaw represents a classic buffer overflow condition where the shift count parameter is not properly bounded.
The operational impact of this vulnerability is significant as it allows attackers to potentially trigger kernel panics or execute arbitrary code within the kernel context through crafted netfilter rules. Since the validation occurs too late in the packet processing pipeline, malicious rules can remain undetected until they are actually processed during packet evaluation. This creates a remote code execution vector where an attacker with network access and the ability to modify firewall rules could exploit this condition to compromise system integrity.
Mitigation strategies include implementing early validation of shift operands within the u32_mt_checkentry() function to reject malformed rules before they enter the packet processing path. The fix requires checking XT_U32_LEFTSH and XT_U32_RIGHTSH operands for valid range constraints, specifically ensuring shift counts remain within 0-31 bit boundaries for 32-bit operations. This approach aligns with ATT&CK technique T1548.001 for privilege escalation through kernel exploitation. System administrators should also implement proper rule validation and monitoring of firewall configurations to prevent malformed rules from being loaded into the kernel's netfilter subsystem, as recommended by the National Institute of Standards and Technology cybersecurity framework for kernel-level vulnerability management.
The vulnerability demonstrates the critical importance of input validation in kernel space operations where malformed data can lead to catastrophic system failures. Proper bounds checking and early validation mechanisms are essential to prevent out-of-bounds operations that could compromise entire systems through privilege escalation attacks. This flaw underscores the need for comprehensive security testing of kernel modules and the implementation of robust defensive programming practices to protect against undefined behavior in low-level system components.