CVE-2023-0179: Linux Kernel Buffer Overflow Vulnerability

CVE-2023-0179 Overview

CVE-2023-0179 is a buffer overflow vulnerability in the Netfilter subsystem of the Linux Kernel. The flaw resides in the nft_payload code path and stems from an integer underflow [CWE-190] when processing VLAN headers. A local, authenticated attacker can exploit the issue to leak both stack and heap addresses, defeating Kernel Address Space Layout Randomization (KASLR). Successful exploitation enables arbitrary code execution in kernel context and local privilege escalation to root. The vulnerability affects multiple Linux distributions, including Ubuntu 16.04 through 22.04 LTS, Fedora 36 and 37, and Red Hat Enterprise Linux 9.0 variants.

Critical Impact
Local attackers with unprivileged user namespace access can escalate to root, gaining full control over the affected Linux system.

Affected Products

Linux Kernel (multiple versions prior to the upstream fix)
Canonical Ubuntu Linux 16.04, 18.04, 20.04, and 22.04 LTS
Red Hat Enterprise Linux 9.0 (including EUS, Server, Real Time, and IBM Z / Power LE variants)

Discovery Timeline

2023-03-27 - CVE-2023-0179 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-0179

Vulnerability Analysis

The vulnerability lives in the Netfilter nf_tables component, specifically in the nft_payload_copy_vlan function used by the nft_payload expression. When the kernel reconstructs a VLAN-tagged packet header for inspection, it performs arithmetic on user-influenced length fields without sufficient validation. An integer underflow occurs, which is then used as a size argument in a subsequent memory copy operation.

The resulting out-of-bounds write corrupts adjacent kernel memory. Attackers can shape the surrounding heap layout to overwrite function pointers or other control structures. The bug also enables an information disclosure primitive that leaks both stack and heap addresses, breaking KASLR and enabling reliable exploit construction.

Root Cause

The root cause is an integer underflow [CWE-190] in length arithmetic within nft_payload_copy_vlan. The kernel computes a destination offset and copy length based on attacker-controllable VLAN metadata. When specific values are supplied, the computation wraps around and produces an unexpectedly large length, leading to a buffer overflow during the subsequent header copy.

Attack Vector

Exploitation requires local access and the ability to create or manipulate nf_tables rules. On distributions that allow unprivileged user namespaces, any local user can obtain CAP_NET_ADMIN inside a new namespace and craft malicious netlink messages to install vulnerable rules. The attacker then triggers packet processing through the crafted rule to invoke the underflow and overwrite kernel memory. Further technical analysis is available in the Red Hat Bugzilla Report and the OSS-Sec Mailing List Discussion.

Detection Methods for CVE-2023-0179

Indicators of Compromise

Unexpected nft_payload or nf_tables rule creation by unprivileged users
Processes invoking unshare(CLONE_NEWUSER | CLONE_NEWNET) followed by netlink writes to NFNL_SUBSYS_NFTABLES
Kernel oops or warning messages referencing nft_payload_copy_vlan or netfilter slab corruption
New root shells or SUID binary creation spawned from previously unprivileged user contexts

Detection Strategies

Audit execve and unshare syscall telemetry for user namespace creation chained with netfilter manipulation
Monitor netlink socket activity on AF_NETLINK family 12 (NETLINK_NETFILTER) from non-administrative processes
Inspect /var/log/kern.log and dmesg output for KASAN or slab corruption reports involving netfilter symbols
Correlate unexpected UID transitions to root with prior container, sandbox, or unprivileged shell activity

Monitoring Recommendations

Enable auditd rules covering the unshare, setns, and clone syscalls with CLONE_NEWUSER flags
Forward kernel ring buffer events to a centralized logging pipeline for anomaly review
Track nft and iptables-nft command execution by non-root users across the fleet
Baseline normal netfilter rule churn so that bursts of rule creation surface as anomalies

How to Mitigate CVE-2023-0179

Immediate Actions Required

Apply the latest kernel updates from your distribution vendor for Ubuntu, Fedora, and Red Hat Enterprise Linux 9.0
Disable unprivileged user namespaces where not required by setting kernel.unprivileged_userns_clone=0 on Debian and Ubuntu systems
Restrict use of the nf_tables module on systems that do not require it, using module blacklisting
Inventory affected hosts and prioritize patching for multi-tenant systems, container hosts, and shared developer workstations

Patch Information

The upstream fix corrects the integer underflow in nft_payload_copy_vlan by validating length arithmetic before invoking the memory copy. Distribution-specific updates are available through the Packet Storm Security Notice for Ubuntu live patch users, the Red Hat Bugzilla Report for RHEL 9.0, and the NetApp Security Advisory for affected appliances.

Workarounds

Set sysctl -w kernel.unprivileged_userns_clone=0 to block unprivileged namespace creation on supported kernels
Add install nf_tables /bin/true to /etc/modprobe.d/ to prevent loading of the vulnerable module on hosts that do not need it
Restrict CAP_NET_ADMIN through seccomp or AppArmor profiles for untrusted workloads and container runtimes
Use a kernel live-patching service to apply the fix without rebooting production systems

bash

# Configuration example: harden against local Netfilter exploits
echo 'kernel.unprivileged_userns_clone=0' | sudo tee /etc/sysctl.d/99-cve-2023-0179.conf
sudo sysctl --system

# Optionally blacklist nf_tables on hosts that do not require it
echo 'install nf_tables /bin/true' | sudo tee /etc/modprobe.d/blacklist-nftables.conf

# Verify current kernel version after patching
uname -r