CVE-2021-3501: 
Linux Kernel vulnerability analysis and mitigation

A flaw was discovered in the Linux kernel versions before 5.12, identified as CVE-2021-3501. The vulnerability exists in the KVM API where the value of internal.ndata is mapped to an array index, which can be updated by a user process at any time. This vulnerability was discovered by Reiji Watanabe from Google and was publicly disclosed on April 15, 2021 (RedHat Bugzilla, NVD).

The vulnerability occurs in the _vmxhandle_exit() function where vcpu->run->internal.ndata is used as an array index. Since vcpu->run can be mapped to user address space with write permissions, the 'ndata' value could be manipulated by user processes to point outside the bounds of the array, leading to an out-of-bounds write condition. The vulnerability has been assigned a CVSS v3.1 base score of 7.1 (HIGH) with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H (NVD).

The primary impact of this vulnerability affects data integrity and system availability. A successful exploitation could allow a local attacker to cause a denial of service (system crash) or potentially execute arbitrary code. The vulnerability requires local access and low privileges to exploit (Ubuntu Security).

The vulnerability was fixed in Linux kernel version 5.12 through a patch that modifies how the ndata value is handled in the _vmxhandle_exit() function. The fix involves using a local variable instead of directly accessing the user-modifiable data structure. The patch was committed with ID 04c4f2ee3f68c9a4bf1653d15f1a9a435ae33f7a (Kernel Commit).