CVE-2023-39197: Linux Kernel Information Disclosure Flaw

CVE-2023-39197 Overview

CVE-2023-39197 is an out-of-bounds read vulnerability in the Netfilter Connection Tracking (conntrack) subsystem of the Linux kernel. The flaw affects DCCP (Datagram Congestion Control Protocol) packet handling within the kernel's connection tracking code. A remote attacker can exploit this issue without authentication or user interaction to disclose sensitive kernel memory contents. The vulnerability is classified as [CWE-125] Out-of-Bounds Read and impacts Linux kernel builds shipped by major distributions, including Fedora 38.

Critical Impact
Remote, unauthenticated attackers can leak sensitive kernel memory by sending crafted DCCP traffic to systems running affected Linux kernel versions with Netfilter connection tracking enabled.

Affected Products

Linux Kernel (multiple versions with Netfilter conntrack DCCP support)
Fedora 38
Red Hat Enterprise Linux derivatives shipping affected kernel builds

Discovery Timeline

2024-01-23 - CVE-2023-39197 published to the National Vulnerability Database (NVD)
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-39197

Vulnerability Analysis

The vulnerability resides in the Netfilter connection tracking module, which maintains state information for network connections traversing the Linux kernel. The bug occurs in the DCCP protocol handler within conntrack. When parsing DCCP packets, the kernel reads beyond the bounds of the intended buffer, exposing adjacent kernel memory.

DCCP is a transport-layer protocol designed for congestion-controlled, unreliable datagram flows. The Netfilter connection tracking layer parses DCCP headers to extract state information for stateful firewall rules and NAT translation. Insufficient validation of packet length fields against the actual buffer size enables the out-of-bounds read.

The disclosed memory may contain sensitive data such as cryptographic keys, kernel pointers useful for bypassing KASLR, or fragments of other network traffic. The vulnerability does not directly enable code execution or write access. Confidentiality is the primary impact, while integrity and availability remain unaffected.

Root Cause

The root cause is missing or insufficient length validation in the DCCP packet parsing logic of the Netfilter connection tracking subsystem. The handler trusts header-derived offsets without verifying that referenced data falls within the bounds of the socket buffer (skb). When a crafted DCCP packet specifies offsets exceeding the actual packet length, the kernel reads memory outside the allocated buffer.

Attack Vector

An attacker sends specially crafted DCCP packets to a target system running an affected Linux kernel with Netfilter connection tracking active. No authentication, privileges, or user interaction are required. The attack proceeds over the network and triggers the out-of-bounds read in kernel space. The attacker recovers leaked memory contents through response behavior, side channels, or subsequent kernel state observations. Because verified public exploit code is not available, the vulnerability description should be treated as the authoritative technical reference. See the Red Hat CVE-2023-39197 Advisory and Red Hat Bug Report #2218342 for vendor analysis.

Detection Methods for CVE-2023-39197

Indicators of Compromise

Unexpected inbound DCCP traffic (IP protocol number 33) to hosts that do not normally use DCCP
Anomalous DCCP packets with malformed or inconsistent header length fields
Kernel log entries referencing nf_conntrack or DCCP parsing errors
Elevated rates of connection tracking events tied to DCCP flows from a single source

Detection Strategies

Inspect network telemetry for inbound DCCP packets on systems that do not legitimately use DCCP, and treat such traffic as suspicious
Correlate kernel ring buffer messages (dmesg) with network capture data to identify malformed DCCP header parsing events
Apply IDS/IPS signatures targeting DCCP header anomalies, including length fields inconsistent with packet size

Monitoring Recommendations

Monitor /proc/net/nf_conntrack for unusual DCCP state entries originating from external sources
Audit kernel versions across the fleet against the fixed versions listed in vendor advisories
Log and alert on DCCP traffic at perimeter firewalls and host-based packet filters

How to Mitigate CVE-2023-39197

Immediate Actions Required

Apply the kernel update provided by your Linux distribution vendor as soon as it is available
Identify all hosts running affected Linux kernel builds, including Fedora 38, and prioritize internet-facing systems
Block inbound DCCP traffic (IP protocol 33) at perimeter and host firewalls if DCCP is not required

Patch Information

Update to a patched Linux kernel as published by your distribution. Refer to the Red Hat CVE-2023-39197 Advisory for vendor-specific fixed package versions and to the Red Hat Bug Report #2218342 for upstream patch references. Fedora 38 users should apply the latest kernel package via dnf update kernel.

Workarounds

Blacklist the DCCP kernel module if DCCP is not used, preventing nf_conntrack from loading the affected DCCP handler
Drop DCCP packets in iptables/nftables rules at the host level
Restrict inbound DCCP traffic at network ingress points using ACLs on routers and firewalls

bash

# Configuration example: disable DCCP module and block DCCP traffic
echo 'install dccp /bin/true' | sudo tee /etc/modprobe.d/disable-dccp.conf
echo 'install nf_conntrack_dccp /bin/true' | sudo tee -a /etc/modprobe.d/disable-dccp.conf

# Block DCCP (IP protocol 33) at the host firewall
sudo iptables -A INPUT -p 33 -j DROP
sudo ip6tables -A INPUT -p 33 -j DROP