CVE-2022-25636: Linux Kernel Privilege Escalation Flaw

CVE-2022-25636 Overview

CVE-2022-25636 is a heap out-of-bounds write vulnerability in the Linux kernel's netfilter subsystem, specifically within the net/netfilter/nf_dup_netdev.c component. This vulnerability affects Linux kernel versions 5.4 through 5.6.10 and is related to the nf_tables_offload functionality. Local users with limited privileges can exploit this flaw to escalate their privileges on the affected system, potentially gaining root access.

Critical Impact
Local privilege escalation vulnerability allowing authenticated users to gain elevated (root) privileges through a heap out-of-bounds write in the kernel's netfilter subsystem.

Affected Products

Linux Kernel versions 5.4 through 5.6.10
Debian Linux 11.0
NetApp H300E, H300S, H410C, H410S, H500E, H500S, H700E, H700S
Oracle Communications Cloud Native Core Binding Support Function 22.1.3
Oracle Communications Cloud Native Core Network Exposure Function 22.1.1
Oracle Communications Cloud Native Core Policy 22.2.0

Discovery Timeline

2022-02-21 - Vulnerability disclosed via Openwall OSS-Security mailing list
2022-02-24 - CVE CVE-2022-25636 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-25636

Vulnerability Analysis

The vulnerability exists in the netfilter offload functionality within the Linux kernel. When processing network flow rules for hardware offload capabilities, the kernel fails to properly validate array bounds in the nf_dup_netdev.c module. This results in a heap out-of-bounds write condition that can be triggered by a local user with low privileges.

The flaw specifically manifests during the handling of netfilter table rules when offloading is configured. The kernel incorrectly calculates or validates the index used to write data to a heap-allocated buffer, allowing an attacker to write beyond the intended memory region. This memory corruption can be leveraged to overwrite critical kernel data structures, ultimately enabling arbitrary code execution in kernel context.

Root Cause

The root cause is an improper bounds check in the nf_tables_offload code path. When flow rules are being processed for hardware offload, the code in net/netfilter/nf_dup_netdev.c writes to a heap buffer without properly validating the write index. This missing or improper bounds validation allows writes beyond the allocated buffer size, corrupting adjacent heap memory.

The vulnerability is classified under CWE-269 (Improper Privilege Management), as the memory corruption ultimately allows privilege escalation from a low-privileged user to root.

Attack Vector

The attack requires local access to the system with at least low-level user privileges. The attacker must be able to interact with the netfilter subsystem, typically through the nftables interface. No user interaction is required once the attacker has local access.

The exploitation process involves:

Creating specially crafted netfilter rules that trigger the offload code path
Manipulating the flow rule configuration to cause an out-of-bounds write
Carefully controlling the write target to overwrite kernel data structures
Leveraging the corrupted memory to escalate privileges to root

The vulnerability can be exploited without hardware offload support being present, as the code path is triggered during rule processing regardless of actual hardware capabilities. Technical details and proof-of-concept resources are available in the GitHub CVE-2022-25636 Repository and the detailed analysis by Nick Gregory.

Detection Methods for CVE-2022-25636

Indicators of Compromise

Unexpected kernel crashes or panics related to netfilter or nf_tables subsystems
Suspicious process activity from low-privileged users attempting to escalate to root
Unusual nftables rule creation or manipulation activity
Memory corruption artifacts in kernel logs referencing heap or slab allocations

Detection Strategies

Monitor for suspicious nft command executions from non-administrative users
Implement kernel audit rules to track netfilter subsystem access and modifications
Deploy endpoint detection solutions capable of monitoring kernel-level activity
Use SentinelOne's behavioral AI to detect privilege escalation attempts and anomalous process lineage

Monitoring Recommendations

Enable kernel auditing for netfilter and nftables operations using auditd rules
Configure alerting for any process gaining unexpected elevated privileges
Monitor for kernel oops or panic messages referencing nf_dup_netdev or nf_tables_offload
Implement file integrity monitoring on critical system binaries that could be modified post-exploitation

How to Mitigate CVE-2022-25636

Immediate Actions Required

Update the Linux kernel to a patched version that includes commit b1a5983f56e371046dcf164f90bfaf704d2b89f6
Review and restrict user access to nftables functionality where possible
Apply vendor-specific patches from Debian, NetApp, Oracle, or other affected distributions
Consider restricting unprivileged user namespace creation as a defense-in-depth measure

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available in commit b1a5983f56e371046dcf164f90bfaf704d2b89f6 in the Linux Kernel Netfilter Repository.

Distribution-specific patches are available:

Debian: DSA-5095 Security Advisory
NetApp: NetApp Security Advisory NTAP-20220325-0002
Oracle: Oracle Critical Patch Update July 2022
Ubuntu: Kernel Live Patch LSN-0085-1

Workarounds

Restrict access to the nftables interface for non-administrative users using filesystem permissions
Disable unprivileged user namespaces if not required: sysctl -w kernel.unprivileged_userns_clone=0
Use SELinux or AppArmor policies to limit netfilter access to trusted processes only
Monitor and limit CAP_NET_ADMIN capability assignments to trusted users and processes

bash

# Disable unprivileged user namespaces as defense-in-depth
echo "kernel.unprivileged_userns_clone = 0" >> /etc/sysctl.conf
sysctl -p

# Add audit rules for nftables monitoring
auditctl -w /usr/sbin/nft -p x -k nftables_exec
auditctl -a always,exit -F arch=b64 -S socket -F a0=16 -k netfilter_socket