CVE-2026-53092: Linux Kernel Privilege Escalation Flaw

CVE-2026-53092 Overview

CVE-2026-53092 is a Linux kernel vulnerability in the Berkeley Packet Filter (BPF) verifier. The flaw resides in adjust_reg_min_max_vals(), where the verifier mishandles arithmetic operations of the form rX += rX when src_reg and dst_reg point to the same bpf_reg_state. The verifier modifies dst_reg in place, then later reads src_reg using is_reg_const() and reg_const_value(), obtaining the already-mutated post-operation value instead of the original source value.

The result is an incorrect delta that sync_linked_regs() propagates to linked registers, producing a verifier-versus-runtime mismatch. The upstream fix skips this corner case in the delta tracking logic.

Critical Impact
A verifier-versus-runtime mismatch in BPF register tracking can allow a crafted BPF program to violate the verifier's safety assumptions at runtime, potentially leading to out-of-bounds access in kernel context.

Affected Products

Linux kernel (BPF subsystem, kernel/bpf/verifier.c)
Stable kernel branches prior to commits cc86a8b0a1c5, d7f14173c0d5, and d88e8e4a3b52
Distributions shipping affected stable kernels with eBPF enabled

Discovery Timeline

2026-06-24 - CVE-2026-53092 published to NVD
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-53092

Vulnerability Analysis

The BPF verifier statically tracks the possible value ranges of every register before allowing a program to load. When two operands of an ALU operation are aliased to the same bpf_reg_state, the verifier must reason about a single underlying state. adjust_reg_min_max_vals() first mutates the destination register, then proceeds to additional bookkeeping for linked-register delta propagation. That bookkeeping invokes is_reg_const(src_reg) and reg_const_value(src_reg) to derive a constant delta, but because src_reg == dst_reg, the read returns the post-arithmetic value rather than the original source value.

The miscalculated delta is then propagated through sync_linked_regs() to every register linked to the same state. Linked registers receive an offset that no longer corresponds to the program's actual runtime behavior, meaning the verifier's tracked bounds diverge from the values the CPU computes during execution.

Root Cause

The root cause is an ordering and aliasing bug in adjust_reg_min_max_vals(). The function does not account for the case where the source and destination operands reference the same register state. Reading the source after the destination has been modified violates the implicit assumption that source values remain stable through delta computation. The patches address this by skipping linked-register delta tracking entirely when src_reg == dst_reg.

Attack Vector

Exploitation requires the ability to load BPF programs. On systems where unprivileged BPF is disabled (kernel.unprivileged_bpf_disabled=1), an attacker needs CAP_BPF or CAP_SYS_ADMIN. A crafted program uses rX += rX (or analogous aliased arithmetic) to coerce the verifier into computing incorrect bounds for linked registers. At runtime the registers hold values outside those bounds, enabling memory accesses the verifier believed were safe. The verifier-runtime mismatch is the foundation for kernel memory corruption or information disclosure in the BPF execution context.

No public proof-of-concept is referenced in the advisory. The vulnerability mechanism is detailed in the upstream commits cc86a8b0a1c5, d7f14173c0d5, and d88e8e4a3b52.

Detection Methods for CVE-2026-53092

Indicators of Compromise

Unexpected BPF program loads from non-administrative users or containers, particularly programs containing aliased ALU operations.
Kernel logs reporting verifier anomalies, BPF JIT errors, or unexplained oops events in BPF execution paths.
Anomalous bpf() syscall volume from workloads that historically do not use eBPF.

Detection Strategies

Audit bpf() syscall usage with the BPF_PROG_LOAD command across hosts and correlate with the loading UID and capability set.
Compare running kernel versions against the patched stable commits and flag hosts on vulnerable releases with kernel.unprivileged_bpf_disabled=0.
Inspect BPF program bytecode collected via bpftool prog dump xlated for arithmetic instructions where source and destination registers are identical.

Monitoring Recommendations

Enable kernel audit rules for the bpf syscall and forward events to a centralized log platform for retention and analysis.
Track CAP_BPF and CAP_SYS_ADMIN grants in container and workload manifests and alert on additions.
Monitor kernel ring buffer (dmesg) for verifier rejections and JIT-related warnings that may indicate exploitation attempts.

How to Mitigate CVE-2026-53092

Immediate Actions Required

Apply the upstream stable kernel updates containing commits cc86a8b0a1c5, d7f14173c0d5, and d88e8e4a3b52, then reboot affected hosts.
Set kernel.unprivileged_bpf_disabled=1 on systems where unprivileged BPF is not required.
Restrict CAP_BPF and CAP_SYS_ADMIN to trusted workloads only, particularly in multi-tenant container environments.

Patch Information

The fix is distributed across three Linux stable tree commits referenced in the NVD entry. Vendors of enterprise Linux distributions typically backport BPF verifier fixes to their long-term support kernels. Consult your distribution's security tracker for the specific kernel package version containing the backport, and validate the running kernel reflects the patched build after deployment.

Workarounds

Disable unprivileged BPF program loading via the kernel.unprivileged_bpf_disabled sysctl until patches are applied.
Use Linux Security Modules such as SELinux or AppArmor to deny the bpf syscall to untrusted processes and containers.
Remove CAP_BPF from container security contexts and Kubernetes pod specifications where eBPF is not required.

bash

# Disable unprivileged BPF until kernel is patched
sysctl -w kernel.unprivileged_bpf_disabled=1
echo 'kernel.unprivileged_bpf_disabled=1' >> /etc/sysctl.d/90-bpf-hardening.conf

# Verify running kernel and audit bpf() syscall usage
uname -r
auditctl -a always,exit -F arch=b64 -S bpf -k bpf_syscall