CVE-2020-27170

What it actually does

The flaw performs undesirable out-of-bounds speculation on pointer arithmetic in kernel/bpf/verifier.c for pointer types without a defined ptr_limit, enabling side-channel attacks that defeat Spectre mitigations and leak sensitive kernel memory.

Why it matters to the business

Attackers with local access could extract confidential kernel data on Linux systems, increasing risk of information disclosure in environments relying on BPF functionality.

How an attack unfolds

An attacker with local access loads a crafted BPF program using pointer arithmetic on types lacking ptr_limit to trigger speculative out-of-bounds reads, then employs side-channel techniques to bypass Spectre protections and obtain kernel memory contents.

How to fix it

Update the Linux kernel to a version containing commit f232326f6966cf2a1d1db7bc917a4ce5f9f55f76 or later, such as 5.11.8 or newer releases incorporating the fix.

How to confirm the fix worked

Confirm the running kernel version is 5.11.8 or higher, or verify presence of commit f232326f6966cf2a1d1db7bc917a4ce5f9f55f76 in the source.

Typical attack path

1. Obtain local access on a vulnerable Linux system
2. Load a malicious BPF program triggering pointer arithmetic speculation
3. Exploit side-channel leakage to read kernel memory despite mitigations

How to detect it

Review kernel logs and audit trails for unusual BPF verifier or program load events that might indicate attempts to exploit speculative execution paths.

What your security team should do

• Apply kernel updates to incorporate the fix as soon as possible
• Restrict unprivileged BPF program loading where feasible
• Monitor kernel audit logs for anomalous BPF activity