CVE-2024-56569

What it actually does

Null pointer dereference in ftrace stack_trace_filter handling of mod: commands, triggered when processing module filters such as write*:mod:ext3, leading to kernel crash.

Why it matters to the business

System instability or denial of service on affected Linux kernel versions, with potential operational disruption for organizations running legacy Ubuntu kernels; low exploit likelihood reduces immediate risk but patching remains necessary for stability.

How an attack unfolds

An attacker with sufficient privileges writes a crafted filter string containing a mod: directive to the stack_trace_filter sysfs file, triggering the unhandled corner case that results in a null pointer dereference and kernel panic.

How to fix it

Upgrade affected packages to the listed fixed versions: linux 3.13.0-86.130 or 4.4.0-22.39, linux-aws 4.4.0-1002.2 or 4.4.0-1001.10, linux-lts-xenial 4.4.0-22.39~14.04.1, linux-gke 4.4.0-1003.3, linux-hwe 4.8.0-36.36~16.04.1, linux-raspi2 4.4.0-1010.12, linux-snapdragon 4.4.0-1013.14, linux-lts-vivid 3.19.0-59.65~14.04.1, linux-lts-wily 4.2.0-36.41~14.04.1.

How to confirm the fix worked

Verify kernel and package versions match or exceed the fixed releases; attempt the reproducer command in a test environment and confirm absence of crash; review ftrace module filter handling in source.

Typical attack path

1. Obtain local or privileged access to the target system
2. Identify presence of /sys/kernel/tracing/stack_trace_filter
3. Execute echo command with mod: syntax targeting a module
4. Trigger null pointer dereference causing kernel crash

How to detect it

Review system logs for kernel oops or panic entries around ftrace or stack_trace_filter; inspect command history for mod: usage in tracing filter files; correlate with known threat actor patterns involving Linux kernel resource issues.

What your security team should do

• Prioritize upgrades for internet-facing or critical systems using listed affected Ubuntu kernels
• Apply fixed package versions immediately on legacy 14.04/16.04 deployments
• Monitor EPSS trend and threat actor reports for any increase in exploitation activity
• Restrict write access to tracing sysfs files where possible