CVE-2025-71203 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
riscv: Sanitize syscall table indexing under speculation
The syscall number is a user-controlled value used to index into the syscall table. Use array_index_nospec() to clamp this value after the bounds check to prevent speculative out-of-bounds access and subsequent data leakage via cache side channels.
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Analysis
by VulDB Data Team • 05/06/2026
The vulnerability identified as CVE-2025-71203 affects the Linux kernel's implementation of system call handling on RISC-V architecture platforms. This issue represents a critical security flaw that arises from improper bounds checking during system call table access operations. The vulnerability specifically impacts the kernel's handling of user-supplied system call numbers that are used to index into internal syscall tables. When a user process provides a system call number, the kernel must validate this value against acceptable ranges before using it to access kernel memory structures. The flaw occurs when the kernel performs bounds checking but fails to properly sanitize the indexing operation under speculative execution conditions.
The technical root cause of this vulnerability stems from the absence of proper speculation sanitization mechanisms when processing user-controlled indices into kernel data structures. During speculative execution, the processor may execute instructions based on predicted values before the actual bounds checking completes. In this scenario, if a malicious user provides a system call number that exceeds valid bounds, the kernel's bounds checking logic may not adequately prevent speculative access to memory locations outside the intended syscall table boundaries. This creates a potential cache side-channel attack vector where sensitive kernel data could be indirectly accessed and leaked through cache state manipulation.
The operational impact of this vulnerability extends beyond simple privilege escalation or denial of service scenarios. Attackers could potentially exploit this weakness to extract confidential kernel memory contents through sophisticated cache timing attacks, particularly targeting information such as kernel stack contents, memory layout details, or other sensitive data structures. The vulnerability affects systems running Linux kernels on RISC-V processors where speculative execution is enabled, making it relevant to a growing number of embedded systems, servers, and cloud infrastructure platforms transitioning to RISC-V architectures. This issue directly relates to CWE-129, which describes improper validation of array index values, and more specifically to CWE-1306, which addresses the lack of proper bounds checking in speculative execution contexts.
The fix implemented for CVE-2025-71203 involves the introduction of array_index_nospec() function calls to properly clamp user-controlled indices after bounds verification. This approach specifically addresses the speculative execution vulnerability by ensuring that even if speculative execution occurs with an out-of-bounds index value, the actual memory access will be properly constrained to valid array boundaries. The solution aligns with ATT&CK technique T1068 by preventing unauthorized system access through kernel exploitation, and T1106 by maintaining proper system call handling integrity. The mitigation strategy requires kernel updates that implement this sanitization approach across all RISC-V kernel implementations, ensuring that user-supplied system call numbers are properly validated and constrained during both regular and speculative execution phases. This fix demonstrates the importance of considering speculative execution behaviors in kernel security design and represents a standard practice for protecting against cache-based side-channel information leakage vulnerabilities.