CVE-2026-64354: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-64354 Overview

CVE-2026-64354 is a Linux kernel vulnerability in the Berkeley Packet Filter (BPF) subsystem. The flaw resides in btf_parse_struct_metas(), which processes user-supplied BPF Type Format (BTF) data during the BPF_BTF_LOAD operation. A u32 arithmetic wraparound in the remaining-capacity check allows btf_repeat_fields() to expand more fields than the fixed BTF_FIELDS_MAX scratch array can hold. A subsequent memcpy() then writes past the end of the array, corrupting adjacent kernel memory.

Critical Impact
A local user with permission to load BTF blobs can trigger a heap out-of-bounds write in the Linux kernel, leading to memory corruption, privilege escalation, or denial of service.

Affected Products

Linux kernel versions containing the vulnerable btf_repeat_fields() expansion logic
Distributions shipping BPF-enabled kernels prior to the referenced stable commits
Systems permitting unprivileged or capability-holding processes to invoke BPF_BTF_LOAD

Discovery Timeline

2026-07-25 - CVE-2026-64354 published to NVD
2026-07-27 - Last updated in NVD database

Technical Details for CVE-2026-64354

Vulnerability Analysis

The vulnerability is an integer overflow leading to a heap out-of-bounds write [CWE-190, CWE-787] in the Linux kernel BPF subsystem. During BPF_BTF_LOAD, btf_parse_struct_metas() walks user-supplied BTF and calls btf_repeat_fields() to expand repeatable fields from array elements into the fixed-size BTF_FIELDS_MAX scratch array consumed by btf_parse_fields().

The remaining-capacity check computes the expanded field count using unsigned 32-bit arithmetic. A malformed BTF blob can supply values that wrap the multiplication or addition. The wrapped result appears smaller than the scratch capacity, so the check passes even when the true expanded count exceeds BTF_FIELDS_MAX.

Once the check succeeds, the subsequent memcpy() copies the oversized field set into the scratch array, writing past its end and corrupting adjacent kernel memory.

Root Cause

The root cause is missing overflow-safe arithmetic. The capacity check multiplies the number of array elements by the number of repeatable fields per element without using checked math. When the product overflows u32, the truncated result silently passes the bounds validation.

Attack Vector

Exploitation requires local access and the ability to invoke the BPF_BTF_LOAD syscall path. An attacker crafts a malformed BTF blob whose field expansion arithmetic wraps in u32. Loading the blob triggers the oversized memcpy() into the scratch buffer, producing a controllable out-of-bounds write in kernel memory that can be shaped into privilege escalation.

No verified exploit code has been published. See the upstream fix commits for technical detail: b9452b594fd3, c5ff816d5f13, cd407de2ef5d, and ff77d013b737.

Detection Methods for CVE-2026-64354

Indicators of Compromise

Unexpected kernel oops, panic, or KASAN slab-out-of-bounds reports referencing btf_parse_struct_metas or btf_repeat_fields
Auditd records of bpf() syscalls with cmd=BPF_BTF_LOAD from unusual or unprivileged users
New setuid binaries, unexpected root shells, or capability changes shortly after BPF activity

Detection Strategies

Enable CONFIG_KASAN in test environments to surface out-of-bounds writes in the BPF verifier path
Correlate bpf() syscall telemetry with subsequent privilege changes or process anomalies
Monitor dmesg for BTF parsing errors and kernel warnings from the BPF subsystem

Monitoring Recommendations

Ingest kernel audit logs into a central SIEM and alert on high-frequency BPF_BTF_LOAD calls from non-root UIDs
Track processes that hold CAP_BPF or CAP_SYS_ADMIN and load BTF from user-controlled paths
Baseline normal BPF program loading activity per host and alert on deviations

How to Mitigate CVE-2026-64354

Immediate Actions Required

Apply the upstream kernel patches referenced in the stable commits and reboot affected hosts
Restrict BPF_BTF_LOAD access by setting kernel.unprivileged_bpf_disabled=1 where feasible
Audit which users and workloads currently hold CAP_BPF and remove unnecessary grants

Patch Information

The fix replaces the unchecked u32 capacity calculation with checked addition and multiplication and rejects impossible field counts before the memcpy(). Merged stable commits include b9452b594fd3, c5ff816d5f13, cd407de2ef5d, and ff77d013b737. Rebuild the kernel from a patched stable branch or install the vendor update that incorporates these commits.

Workarounds

Set sysctl kernel.unprivileged_bpf_disabled=1 to block BPF loading by unprivileged users
Remove CAP_BPF and CAP_SYS_ADMIN from workloads that do not require BPF program loading
Use seccomp or LSM policies (SELinux, AppArmor) to deny the bpf() syscall for untrusted processes

bash

# Disable unprivileged BPF loading persistently
echo 'kernel.unprivileged_bpf_disabled=1' | sudo tee /etc/sysctl.d/90-bpf-hardening.conf
sudo sysctl --system

# Verify the setting is active
sysctl kernel.unprivileged_bpf_disabled