CVE-2021-3490: 
Linux Kernel vulnerability analysis and mitigation

The eBPF ALU32 bounds tracking vulnerability (CVE-2021-3490) was discovered in the Linux kernel, affecting versions from 5.7-rc1 to versions prior to 5.10.37, 5.11.21, and 5.12.4. The vulnerability stems from improper updating of 32-bit bounds for bitwise operations (AND, OR, and XOR) in the eBPF subsystem. The issue was discovered by Manfred Paul of the RedRocket CTF team and was fixed via commit 049c4e13714e in v5.13-rc4, with backports to stable kernels (Kernel Commit, Ubuntu Security).

The vulnerability exists in the eBPF verifier's scalar32minmax*() functions which incorrectly track 32-bit bounds for bitwise operations. When both source and destination subreg are known constants, the verifier fails to properly update bounds, leading to invalid states where u32minvalue > u32max_value. The AND/OR issues were introduced by commit 3f50f132d840 in 5.7-rc1, while the XOR variant was introduced by commit 2921c90d4718 in 5.10-rc1. The vulnerability received a CVSS v3.1 score of 7.8 (High) with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD).

When successfully exploited, this vulnerability could lead to out-of-bounds reads and writes in the Linux kernel, potentially resulting in arbitrary code execution with kernel privileges. The impact is particularly severe in container environments where it could be used for container escapes and privilege escalation (CrowdStrike).

The primary mitigation is to update affected systems to patched kernel versions (5.10.37, 5.11.21, 5.12.4 or later). For container environments, additional mitigations include: limiting container capabilities (especially CAPBPF and CAPSYS_ADMIN), implementing strong seccomp profiles to restrict dangerous system calls including bpf, and monitoring containerized environments for privileged workloads (NetApp Advisory).

The vulnerability was initially reported through Trend Micro's Zero Day Initiative and was assigned ZDI-CAN-13590. The discovery highlighted the ongoing security challenges in container environments and the importance of proper bounds checking in kernel subsystems (OSS Security).