CVE-2024-50220

What it actually does

The vulnerability allows dup_userfaultfd_complete() to invoke registered UFFD_EVENT_FORK handlers and clear fork contexts even when fork encounters an error, exposing an incompletely initialized or inconsistent maple-tree-backed address space to userland.

Why it matters to the business

Applications relying on userfaultfd may observe inconsistent memory state during failed forks, leading to application crashes, unexpected memory behavior, or degraded stability in containerized and multi-process workloads on affected Linux kernels.

How an attack unfolds

An attacker registers a userfaultfd on VMAs, triggers a fork that fails partway through (for example via resource limits or maple-tree duplication errors), and receives an UFFD_EVENT_FORK event referencing an incompletely built child mm; this can be leveraged by espionage or financially motivated actors listed in recent Linux kernel exploitation campaigns to induce memory corruption or denial of service.

How to fix it

Upgrade affected packages to the fixed versions provided: openssl (Ubuntu 14.04 LTS) to 1.0.1f-1ubuntu2.16, openjdk-7 (Ubuntu 14.04 LTS) to 7u95-2.6.4-0ubuntu0.14.04.1, and gnutls26 (Ubuntu 14.04 LTS) to 2.12.23-12ubuntu2.4; apply the corresponding kernel update that includes commit d24062914837 and the dup_userfaultfd_fail() rollback logic.

How to confirm the fix worked

Confirm the running kernel contains the patch that defers khugepaged/ksm and adds the error-path call to dup_userfaultfd_fail(); verify package versions match the listed fixed releases and test fork under error conditions while userfaultfd is registered.

Typical attack path

1. Register userfaultfd on target process VMAs
2. Force a fork operation that encounters an error before mm duplication completes
3. Receive UFFD_EVENT_FORK event via dup_fctx() on the still-inconsistent child address space
4. Interact with the malformed VMA state to trigger memory corruption or crash

How to detect it

Search kernel logs and audit trails for unexpected userfaultfd fork events followed by process crashes or memory errors; correlate with threat-actor TTPs around Linux kernel out-of-bounds and uninitialized-resource issues.

What your security team should do

• Prioritize kernel and listed package updates on all Ubuntu 14.04 LTS systems within normal change windows given low EPSS and non-KEV status
• Monitor for any downstream dependents using older kernel builds
• Review userfaultfd usage in critical services and ensure error handling around fork
• Add the supplied fixed versions to patch-management automation