CVE-2025-40050 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
bpf: Skip scalar adjustment for BPF_NEG if dst is a pointer
In check_alu_op(), the verifier currently calls check_reg_arg() and adjust_scalar_min_max_vals() unconditionally for BPF_NEG operations. However, if the destination register holds a pointer, these scalar adjustments are unnecessary and potentially incorrect.
This patch adds a check to skip the adjustment logic when the destination register contains a pointer.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability described in CVE-2025-40050 resides within the Linux kernel's eBPF (extended Berkeley Packet Filter) verifier component, specifically affecting how the kernel handles arithmetic operations on BPF_NEG instructions. This issue represents a subtle but significant flaw in the kernel's validation logic that could potentially lead to incorrect program execution or unexpected behavior in kernel-space programs. The eBPF subsystem serves as a critical component for network filtering, tracing, and system monitoring within the Linux kernel, making this vulnerability particularly concerning from a security perspective.
The technical flaw manifests in the check_alu_op() function where the verifier performs scalar adjustments for BPF_NEG operations without proper consideration of the destination register's type. When a BPF_NEG instruction operates on a pointer value, the current implementation incorrectly applies scalar adjustment logic that is designed for integer arithmetic operations. This mismatch occurs because the verifier unconditionally calls check_reg_arg() and adjust_scalar_min_max_vals() functions regardless of whether the destination register contains a pointer or scalar value. The scalar adjustment logic is fundamentally incompatible with pointer arithmetic operations, as it attempts to modify pointer values using scalar mathematical operations that could result in invalid memory addresses or corrupted program state.
The operational impact of this vulnerability extends beyond simple incorrect arithmetic operations, as it affects the fundamental correctness of the eBPF verifier's type checking system. When the destination register contains a pointer value, applying scalar adjustments could lead to unpredictable behavior in kernel-space programs that rely on eBPF for system monitoring, network filtering, or performance tracing. This vulnerability could potentially be exploited to bypass security controls or cause system instability, particularly in environments where eBPF programs are used extensively for security monitoring or network packet filtering. The issue is particularly dangerous because it operates at the kernel level where incorrect behavior could compromise the entire system's security posture.
The fix implemented in this patch addresses the root cause by adding a conditional check that specifically identifies when the destination register contains a pointer type. When such a condition is detected, the verifier skips the scalar adjustment logic entirely, preventing the application of inappropriate scalar operations to pointer values. This approach aligns with the principle of least privilege and proper type safety enforcement within kernel space. The solution follows established security practices by ensuring that operations are only performed on data types that support those operations, thereby preventing potential exploitation vectors. This vulnerability demonstrates the importance of proper type checking in kernel-level code and highlights how seemingly minor implementation flaws can have significant security implications. The fix represents a targeted correction that maintains the integrity of the eBPF verifier while preserving all legitimate functionality for scalar operations. This type of vulnerability is classified under CWE-682 Incorrect Arithmetic and relates to the ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, though in kernel context rather than user-space applications. The patch effectively prevents the verifier from applying inappropriate scalar operations to pointer types, maintaining the integrity of kernel memory management and preventing potential exploitation scenarios.