CVE-2025-21785

CVE-2025-21785 is a vulnerability in the Linux kernel's arm64 cacheinfo subsystem that leads to an out-of-bounds write in the cacheinfo array. The issue arises during the loop that detects and populates cache information, which includes a bounds check on the array size but fails to account for cache levels with separate data and instruction caches. As a result, the index is not properly incremented for populated leaves, potentially allowing writes beyond the array bounds. The vulnerability is classified under CWE-787 (Out-of-bounds Write) with a CVSS v3.1 base score of 7.8.

A local attacker with low privileges (PR:L) can exploit this vulnerability with low complexity (AC:L) and no user interaction required (UI:N), requiring only local access (AV:L) to the system. Successful exploitation could result in high impacts on confidentiality, integrity, and availability (C:H/I:H/A:H), potentially enabling arbitrary code execution, data corruption, or system crashes due to the out-of-bounds write.

Mitigation involves applying the upstream patches referenced in the stable kernel repositories, such as commits 4371ac7b494e, 4ff25f0b18d1, 67b99a2b5811, 715eb1af64779, and 875d742cf532. These fixes resolve the issue by modifying the loop to increment the index for any populated leaf rather than any populated level, ensuring proper bounds handling for separate data and instruction caches. Security practitioners should update affected Linux kernels, particularly those using arm64 architectures, to the patched versions.