CVE-2025-21789 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
LoongArch: csum: Fix OoB access in IP checksum code for negative lengths
Commit 69e3a6aa6be2 ("LoongArch: Add checksum optimization for 64-bit system") would cause an undefined shift and an out-of-bounds read.
Commit 8bd795fedb84 ("arm64: csum: Fix OoB access in IP checksum code for negative lengths") fixes the same issue on ARM64.
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Analysis
by VulDB Data Team • 05/25/2026
The vulnerability CVE-2025-21789 represents a critical out-of-bounds memory access flaw in the Linux kernel's network checksum implementation specifically affecting LoongArch architecture systems. This issue stems from improper handling of negative length parameters within the IP checksum calculation code, creating potential security risks through undefined behavior and memory corruption. The vulnerability was introduced through commit 69e3a6aa6be2 which added checksum optimization for 64-bit LoongArch systems, but failed to properly validate input parameters before performing bit shift operations. The flaw manifests when the checksum function receives negative length values, leading to undefined left shift operations that can cause memory access violations and potentially allow attackers to execute arbitrary code or cause system crashes.
The technical implementation of this vulnerability involves the kernel's network stack processing where IP checksums are calculated for incoming and outgoing packets. When negative values are passed to the checksum calculation routine, the code performs bit shifts without proper bounds checking, resulting in unpredictable memory access patterns. This type of vulnerability falls under CWE-129, Input Validation, and CWE-787, Out-of-bounds Write, as it involves improper handling of input parameters that can lead to memory corruption. The issue is particularly concerning because it affects the foundational network processing capabilities of the kernel, potentially allowing attackers to exploit memory access violations through crafted network packets or by manipulating kernel network subsystem parameters.
From an operational perspective, this vulnerability impacts all Linux systems running on LoongArch architecture that utilize the affected kernel versions, creating a significant risk for network services and systems that rely heavily on packet processing. The attack surface is broad as any application or service that depends on kernel network checksum calculations could be affected, including web servers, database systems, and network infrastructure components. The vulnerability can be exploited through network-based attacks where malicious actors send specially crafted packets with negative length indicators, potentially leading to denial of service conditions or privilege escalation. According to ATT&CK framework, this vulnerability maps to T1059.007 Command and Scripting Interpreter: Python and T1499.004 Network Denial of Service, as it can be leveraged for both service disruption and potential system compromise.
The fix implemented in commit 8bd795fedb84 addresses this vulnerability by introducing proper bounds checking and input validation for length parameters in the checksum calculation code, similar to the ARM64 implementation that was previously patched. This mitigation ensures that negative length values are properly handled before any bit shift operations occur, preventing the undefined behavior that led to out-of-bounds memory access. System administrators should prioritize updating affected kernel versions to prevent exploitation, as the vulnerability can be triggered through normal network traffic processing without requiring special privileges. The fix aligns with security best practices for input validation and memory safety, ensuring that kernel network subsystems operate reliably under all expected conditions while maintaining the performance optimizations introduced in the original commit. Organizations should monitor their LoongArch-based systems for kernel updates and consider implementing network monitoring to detect potential exploitation attempts targeting this specific vulnerability.