CVE-2024-26621

What it actually does

The flaw forces huge-page alignment for anonymous mappings on 32-bit kernels or compat userspace, which can exhaust the constrained virtual address space and cause allocation failures or crashes.

Why it matters to the business

32-bit Linux systems may experience unexpected application crashes or memory allocation failures after routine upgrades, disrupting workloads that run on older or embedded hardware.

How an attack unfolds

A local, unprivileged attacker maps large anonymous regions; the forced alignment exhausts the 32-bit address space, triggering kernel-level allocation errors that manifest as denial-of-service.

How to fix it

Upgrade to a fixed kernel package listed for each Ubuntu release (for example linux 3.11.0-12.19 on 14.04, 4.4.0-2.16 on 16.04, 4.13.0-16.19 on 18.04, 5.4.0-9.12 on 20.04) and reboot.

How to confirm the fix worked

Verify the running kernel version matches or exceeds the fixed package for the distribution release; confirm /proc/version or uname -r reports the corrected build.

Typical attack path

1. Obtain local shell on affected 32-bit or compat userspace system
2. Issue mmap or malloc calls requesting large anonymous mappings
3. Kernel applies THP boundary alignment from the faulty commit
4. Address space exhaustion triggers allocation failure or OOM killer
5. Target process or system becomes unresponsive

How to detect it

Review kernel logs for allocation failures or OOM events immediately after large mmap operations on 32-bit systems; correlate with presence of the pre-fix kernel version.

What your security team should do

• Prioritize patching of any remaining 32-bit Ubuntu 14.04/16.04/18.04/20.04 systems within standard change windows
• Disable or migrate legacy 32-bit workloads to 64-bit kernels where feasible
• Add kernel version checks to vulnerability scanning and asset inventory