Real-Time eBPF Kernel Telemetry & Sigma Rule Synthesis for Linux Threat Detection

Byline: Syed Zada Abrar
Organization: SentinelReign & Andrax Pentester
Published: May 2026

Executive Summary & Bottom Line Up Front (BLUF)

Legacy Linux detection architectures rely on asynchronous audit log parsers (auditd) or polling userland processes. This introduces noticeable index latency and CPU overhead, creating a dangerous blind spot against modern living-off-the-land (LotL) binaries, eBPF-based rootkits, and container breakout vectors.

This masterclass presents a first-principles engineering framework for compiling standard SigmaHQ YAML detection rules into an abstract syntax tree (AST) that evaluates live Linux kernel tracepoints (sys_enter_execve, sys_enter_bpf, security_file_open) in real time using eBPF (Extended Berkeley Packet Filter). By eliminating userland SIEM index latency, security teams can achieve microsecond-level detection and stateful LSM (Linux Security Module) prevention directly inside the Linux kernel.

1. Pedagogical Architecture & Intuition (Step 0)

The Problem: Log Indexing vs. Live Telemetry Streams

Traditional SIEM detection pipelines operate retroactively:

1. Kernel event occurs -> 2. auditd formats log -> 3. Daemon writes to disk -> 4. Log collector ships to indexer -> 5. SIEM executes query.

+------------------+     +---------------+     +---------------+     +------------------+
| Kernel Tracepoint| --> | Audit Daemon  | --> | Log Indexer   | --> | SIEM Query Engine|
| (sys_enter_exec) |     | (User Space)  |     | (Elastic/SPL) |     | (Delayed Alerts) |
+------------------+     +---------------+     +---------------+     +------------------+

The Solution: eBPF Kernel AST Evaluation

With eBPF kernel event streams, event evaluation occurs in-memory at kernel ring buffer emission:

+------------------+     +-------------------+     +---------------------+
| Kernel Tracepoint| --> | eBPF Ring Buffer  | --> | In-Memory AST Engine| --> [Instant Alert /
| (sys_enter_exec) |     | (BPF_MAP_RINGBUF) |     | (Microsecond Match) |    LSM Prevention]
+------------------+     +-------------------+     +---------------------+

2. Under-the-Hood Mechanics: Field Mapping Matrix

SigmaHQ rules are historically Windows-centric. To evaluate them against Linux kernel tracepoints, an alias rewrite engine translates abstract Sigma fields to eBPF struct fields at parse time:

3. Production eBPF Tracepoint Harness (C / Libbpf)

Below is the annotated C code for attaching an eBPF program to tp/syscalls/sys_enter_execve to capture execution telemetry:

#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

struct exec_event {
    u32 pid;
    u32 ppid;
    u32 uid;
    char filename[256];
    char args[512];
};

struct {
    __uint(type, BPF_MAP_TYPE_RINGBUF);
    __uint(max_entries, 256 * 1024);
} ringbuf SEC(".maps");

SEC("tp/syscalls/sys_enter_execve")
int handle_execve(struct trace_event_raw_sys_enter *ctx)
{
    struct exec_event *event;
    
    // Allocate space in the kernel ring buffer
    event = bpf_ringbuf_reserve(&ringbuf, sizeof(*event), 0);
    if (!event)
        return 0;

    // Capture PID, PPID, and UID directly from kernel context
    u64 pid_tgid = bpf_get_current_pid_tgid();
    event->pid = pid_tgid >> 32;
    event->uid = bpf_get_current_uid_gid();

    // Read binary path from sys_enter_execve argument 0
    const char *filename_ptr = (const char *)BPF_CORE_READ(ctx, args[0]);
    bpf_probe_read_str(event->filename, sizeof(event->filename), filename_ptr);

    // Read argument vector from sys_enter_execve argument 1
    const char **args_ptr = (const char **)BPF_CORE_READ(ctx, args[1]);
    if (args_ptr) {
        bpf_probe_read_str(event->args, sizeof(event->args), args_ptr[0]);
    }

    // Submit event to userland AST evaluation engine
    bpf_ringbuf_submit(event, 0);
    return 0;
}

char _license[] SEC("license") = "GPL";

4. Sigma Rule AST Compilation Engine (Go / Rust Concept)

When loading a Sigma rule like GTFOBins abuse or reverse shell execution, the AST parser compiles condition modifiers (contains, endswith, contains|all) into load-time decision nodes:

title: Suspicious Interactive Shell Spawning via Network Utility
id: 9a2b8e30-ebpf-sigma-2026
status: experimental
description: Detects reverse shell invocation via netcat/bash execution in Linux eBPF telemetry
logsource:
  category: process_creation
  product: linux
detection:
  selection_binary:
    Image|endswith:
      - '/nc'
      - '/ncat'
      - '/netcat'
  selection_args:
    CommandLine|contains:
      - '-e /bin/bash'
      - '-e /bin/sh'
      - '>& /dev/tcp/'
  condition: selection_binary and selection_args
falsepositives:
  - Authorized administrator maintenance scripts
level: high

5. Failure Modes, Edge Cases & Evasion Defense

1. Process Name Spoofing (prctl PR_SET_NAME): Adversaries can overwrite argv[0] or process comm names. Defense: Always extract binary paths from sys_enter_execve register pointers directly rather than reading /proc/PID/comm.
2. eBPF Verifier Instruction Limits: Complex nested regex matches inside kernel space can fail eBPF verifier loading. Defense: Perform fast string matching and static prefix checks inside kernel space, passing heavy regular expression evaluations to the userland ring buffer consumer.
3. High-Frequency Noise: High-volume binary invocations (e.g., git, make, cat) can saturate ring buffers. Defense: Implement an dynamic allowlist engine (allowlist.toml) evaluated at parse time.

6. Summary & Security Hardening Checklist

• Kernel Telemetry: Deploy eBPF tracepoints over legacy auditd logging for sub-millisecond execution tracking.
• Field Alignment: Map Sigma fields (Image, CommandLine) to eBPF struct layouts using parse-time alias rewrites.
• Zero SIEM Latency: Evaluate rules directly against kernel ring buffer event streams to enable real-time detection and LSM block enforcement.

Authored under byline Syed Zada Abrar for Andrax Pentester & SentinelReign.