CVE-2022-42703: Linux Kernel Use-After-Free Vulnerability

CVE-2022-42703 Overview

CVE-2022-42703 is a use-after-free vulnerability in mm/rmap.c of the Linux kernel before version 5.19.7. The flaw stems from leaf anon_vma double reuse during reverse mapping operations in the memory management subsystem. A local attacker with low privileges can trigger the condition to corrupt kernel memory and cause a denial-of-service or potentially escalate further depending on heap state. Google Project Zero researchers documented the issue under Issue #2351 and published a follow-up exploitation analysis. The vulnerability is tracked under [CWE-416] (Use After Free).

Critical Impact
Local unprivileged users can corrupt kernel anonymous VMA structures, leading to system crashes and potential kernel memory corruption usable for privilege escalation research.

Affected Products

Linux Kernel versions prior to 5.19.7
Distributions shipping the affected mm/rmap.c reverse mapping code
Systems using anonymous memory mappings (effectively all Linux installations)

Discovery Timeline

2022-10-09 - CVE-2022-42703 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-42703

Vulnerability Analysis

The vulnerability resides in the Linux kernel reverse mapping (rmap) implementation, specifically in handling of anon_vma (anonymous virtual memory area) structures. The rmap subsystem tracks which virtual memory areas map a given physical page, enabling page reclaim and migration to find all mappings.

In the flawed code path, a leaf anon_vma can be reused twice during VMA merging and forking operations. The double reuse causes the kernel to operate on freed memory, producing a classic use-after-free condition. Google Project Zero published a detailed walkthrough in Exploiting CVE-2022-42703 - Bringing Back the Stack Attack.

Root Cause

The defect is incorrect lifetime management of anon_vma objects when a parent VMA shares its anon_vma with a child after a fork, then both VMAs participate in further splits or merges. The reference counting logic permits a leaf anon_vma to be linked into more than one VMA hierarchy and freed while still referenced. Subsequent access through the dangling pointer dereferences freed slab memory.

Attack Vector

Exploitation requires local access and the ability to execute arbitrary unprivileged code, since the attacker must orchestrate specific sequences of fork(), mmap(), munmap(), and madvise() calls to trigger the race. No user interaction or network access is involved. The attack does not yield direct confidentiality or integrity impact but reliably crashes the kernel and provides a primitive that Project Zero demonstrated could be developed into a kernel exploitation technique.

No verified public proof-of-concept code is referenced in the CVE record beyond the Project Zero technical writeup. See the Linux Kernel Commit #2555283 for the upstream fix.

Detection Methods for CVE-2022-42703

Indicators of Compromise

Unexpected kernel oops or BUG messages referencing anon_vma, rmap, or unlink_anon_vmas in dmesg or /var/log/kern.log
Kernel panics during workloads that heavily fork processes and manipulate anonymous mappings
KASAN reports flagging use-after-free in mm/rmap.c on kernels built with sanitizers

Detection Strategies

Inventory Linux kernel versions across the fleet and flag any host running a kernel earlier than 5.19.7 or an unpatched distribution backport
Monitor for unprivileged processes producing repeated kernel oops events tied to memory management functions
Use auditd rules to record unusual sequences of clone, mmap, and madvise syscalls from a single non-privileged process

Monitoring Recommendations

Forward kern.log and dmesg content to a central logging platform and alert on anon_vma or rmap stack traces
Track process crash frequency on production Linux hosts; sustained kernel faults from a single user warrant investigation
Correlate kernel exception telemetry with the originating process lineage to identify suspicious local activity

How to Mitigate CVE-2022-42703

Immediate Actions Required

Upgrade the Linux kernel to version 5.19.7 or later, or apply the distribution-supplied backport that includes commit 2555283eb40df89945557273121e9393ef9b542b
Reboot affected systems after patching to ensure the running kernel reflects the fix
Restrict local shell access on multi-tenant systems until patching is complete

Patch Information

The upstream fix landed in Linux 5.19.7. Reference the Linux Kernel ChangeLog 5.19.7 and the Linux Kernel Commit #2555283 for the exact change to mm/rmap.c. Major distributions (Red Hat, SUSE, Ubuntu, Debian) shipped backports in their respective stable kernel updates.

Workarounds

No supported kernel-level workaround exists; patching is the only complete remediation
Limit local user accounts and enforce least-privilege policies to reduce the population of users able to attempt the trigger
Apply mandatory access control profiles (SELinux, AppArmor) to constrain processes likely to exercise complex memory operations

bash

# Verify the running kernel version and patch status
uname -r

# On Debian/Ubuntu, install the latest stable kernel
sudo apt-get update && sudo apt-get install --only-upgrade linux-image-generic

# On RHEL/CentOS/Rocky, update the kernel package
sudo dnf update kernel

# Reboot to apply the new kernel
sudo reboot