CVE-2022-1055: Linux Kernel Privilege Escalation Flaw

CVE-2022-1055 Overview

A use-after-free vulnerability exists in the Linux Kernel's tc_new_tfilter function that could allow a local attacker to achieve privilege escalation. This memory corruption flaw occurs within the Traffic Control (TC) subsystem, specifically in the traffic classifier filter creation routine. The exploit requires unprivileged user namespaces to be enabled on the target system, which is a common default configuration on many Linux distributions.

Critical Impact

Local attackers with unprivileged access can exploit this use-after-free vulnerability in the kernel's traffic control subsystem to escalate privileges to root, potentially gaining complete control over affected Linux systems.

Affected Products

• Linux Kernel (versions prior to commit 04c2a47ffb13c29778e2a14e414ad4cb5a5db4b5)
• Red Hat Enterprise Linux 8.0
• Fedora 35
• Canonical Ubuntu Linux 16.04 ESM, 18.04 LTS, 20.04 LTS, 21.10, 22.04 LTS
• NetApp H-Series firmware (H300S, H500S, H700S, H300E, H500E, H700E, H410S, H410C)

Discovery Timeline

• March 29, 2022 - CVE-2022-1055 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-1055

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a critical memory corruption issue where the program continues to reference memory after it has been freed. In the context of tc_new_tfilter, this occurs within the Linux kernel's Traffic Control networking subsystem, which is responsible for managing network traffic scheduling and filtering.

The vulnerability allows a local attacker to manipulate memory that has already been deallocated, potentially corrupting kernel data structures. When exploited successfully, this can lead to arbitrary code execution with kernel privileges, effectively granting the attacker root access to the system.

The attack requires unprivileged user namespaces to be accessible, which allows non-root users to create isolated network namespaces where they can invoke the vulnerable TC functionality. This is a common configuration across modern Linux distributions, making the vulnerability exploitable in many real-world scenarios.

Root Cause

The root cause of this vulnerability lies in improper memory management within the tc_new_tfilter function. The code fails to properly handle object lifecycle management, resulting in a scenario where a reference to a traffic filter object is retained after the object's memory has been freed. Subsequent operations on this dangling pointer can corrupt kernel memory or allow an attacker to control kernel execution flow.

The fix implemented in commit 04c2a47ffb13c29778e2a14e414ad4cb5a5db4b5 addresses this issue by ensuring proper synchronization and reference counting for traffic filter objects, preventing the use-after-free condition from occurring.

Attack Vector

The attack vector is local, requiring an attacker to have authenticated access to the target system. The attacker must be able to create user namespaces and invoke Traffic Control netlink operations. The attack sequence typically involves:

1. Creating an unprivileged user namespace to gain access to network namespace operations
2. Setting up traffic control filters to trigger the vulnerable code path
3. Racing the allocation and deallocation of filter objects to create the use-after-free condition
4. Leveraging the memory corruption to achieve privilege escalation

The vulnerability exploitation demonstrates the risks associated with complex kernel subsystems that interact with user-accessible interfaces through namespaces.

Detection Methods for CVE-2022-1055

Indicators of Compromise

• Unusual activity involving Traffic Control (TC) netlink socket operations from unprivileged users
• Kernel log entries indicating memory corruption or unexpected faults in the cls_api.c or related TC modules
• Suspicious processes creating user namespaces and performing network configuration operations
• System crashes or instability related to networking subsystem operations

Detection Strategies

• Monitor for processes invoking TC netlink operations from within user namespaces
• Implement kernel audit rules to track RTM_NEWTFILTER netlink message creation
• Deploy runtime kernel integrity monitoring to detect memory corruption attempts
• Use Linux Security Modules (LSM) or seccomp to restrict access to sensitive netlink operations

Monitoring Recommendations

• Enable and review kernel audit logs for netlink socket operations
• Monitor for anomalous user namespace creation patterns, particularly in combination with network operations
• Deploy endpoint detection solutions that can identify privilege escalation attempts
• Regularly review system logs for kernel oops or panic events related to networking components

How to Mitigate CVE-2022-1055

Immediate Actions Required

• Update the Linux kernel to a version that includes commit 04c2a47ffb13c29778e2a14e414ad4cb5a5db4b5
• Apply vendor-specific security patches from your distribution (Red Hat, Ubuntu, Fedora, etc.)
• Consider disabling unprivileged user namespaces if not required by workloads
• Restrict access to netlink sockets using seccomp or AppArmor/SELinux policies

Patch Information

The vulnerability has been addressed in the upstream Linux kernel through commit 04c2a47ffb13c29778e2a14e414ad4cb5a5db4b5. Major Linux distributions have released corresponding security updates:

• Red Hat has issued advisories for Enterprise Linux 8.0
• Canonical has released patches for Ubuntu 16.04 ESM, 18.04 LTS, 20.04 LTS, 21.10, and 22.04 LTS
• Fedora 35 has received security updates
• NetApp has issued Security Advisory NTAP-20220506-0007 for affected H-Series devices

For detailed patch information, see the Kernel Commit Record and the Syzkaller Bug Report.

Workarounds

• Disable unprivileged user namespaces by setting kernel.unprivileged_userns_clone=0 via sysctl
• Implement network namespace restrictions using container security policies
• Use seccomp profiles to block netlink operations for untrusted applications
• Deploy mandatory access control (SELinux/AppArmor) policies to limit TC operations

# Disable unprivileged user namespaces (temporary mitigation)
sysctl -w kernel.unprivileged_userns_clone=0

# Make the setting persistent across reboots
echo "kernel.unprivileged_userns_clone=0" >> /etc/sysctl.d/99-disable-userns.conf
sysctl --system