CVE-2025-39846

What it actually does

NULL pointer dereference in __iodyn_find_io_region when pcmcia_make_resource fails, causing a crash inside pci_bus_alloc_resource.

Why it matters to the business

Local denial of service that can crash affected Linux systems, requiring a reboot and interrupting workloads until patched.

How an attack unfolds

An attacker with local access crafts conditions that cause pcmcia_make_resource to return NULL; the missing NULL check then leads to dereference and kernel panic when pci_bus_alloc_resource is called.

How to fix it

Update to the fixed kernel commit b990c8c6ff50649ad3352507398e443b1e3527b2 or Debian ldns packages 1.6.17-4 (or later) on affected releases.

How to confirm the fix worked

Confirm the running kernel contains commit b990c8c6ff50649ad3352507398e443b1e3527b2 or verify ldns package version is at least 1.6.17-4; re-test PCMCIA resource allocation under failure injection.

Typical attack path

1. Obtain local user access on an unpatched Linux system
2. Trigger PCMCIA resource allocation paths that exercise __iodyn_find_io_region
3. Force pcmcia_make_resource failure to produce a NULL res pointer
4. Let pci_bus_alloc_resource dereference the NULL pointer and crash the kernel

How to detect it

Review kernel crash logs and dmesg for NULL pointer dereference traces containing __iodyn_find_io_region or pcmcia_make_resource after local PCMCIA activity.

What your security team should do

• Prioritize patching systems that still expose PCMCIA or related legacy drivers
• Apply the listed fixed kernel or package versions within standard change windows
• Monitor for local crash reports involving pcmcia_make_resource or __iodyn_find_io_region