CVE-2024-56763

What it actually does

The flaw permits a large or zero count value to reach bitmap_parse_user via tracing_cpumask_write without prior validation, triggering a warning and bypassing intended input checks in the kernel tracing subsystem.

Why it matters to the business

Systems running affected kernels may experience unexpected warnings or degraded tracing functionality, increasing operational overhead for diagnostics and potentially affecting performance monitoring in high-scale Linux environments; low exploitability reduces immediate urgency but kernel exposure remains widespread.

How an attack unfolds

An attacker with local access supplies an oversized or zero count to the tracing cpumask interface, causing the unvalidated input to reach bitmap_parse_user and surface a kernel warning that could be chained with other kernel issues; listed threat actors have historically targeted similar Linux kernel input and resource-handling flaws in espionage and financially motivated campaigns.

How to fix it

Upgrade the Linux kernel to a version containing the fix that adds explicit count validation before calling bitmap_parse_user; for chromium-browser on Ubuntu 14.04 LTS apply version 53.0.2785.143-0ubuntu0.14.04.1.1142 or later where the kernel dependency is resolved.

How to confirm the fix worked

Confirm the running kernel contains the tracing_cpumask_write count check, review kernel build logs or source for the added validation, and test by attempting oversized writes to the cpumask interface without triggering warnings.

Typical attack path

1. Locate the tracing cpumask sysfs or proc interface
2. Write an invalid large or zero count value
3. Trigger bitmap_parse_user warning path
4. Observe or leverage resulting kernel behavior

How to detect it

Search kernel logs and dmesg for warnings originating from bitmap_parse_user called via tracing paths; correlate with process activity writing to tracing cpumask files; review audit logs for unusual local writes to kernel tracing interfaces by listed threat actor TTPs.

• bitmap_parse_user
• tracing_cpumask_write
• tracing cpumask

What your security team should do

• Prioritize kernel updates on all Linux hosts given ecosystem prevalence
• Review tracing subsystem usage and restrict unprivileged access where possible
• Monitor EPSS stability and re-evaluate if new exploit code appears