CVE-2023-1075: Linux Kernel Info Disclosure Vulnerability

CVE-2023-1075 Overview

A type confusion vulnerability was discovered in the Linux Kernel's TLS (Transport Layer Security) implementation. The tls_is_tx_ready() function incorrectly checks for list emptiness, which can lead to accessing a type confused entry in the list_head structure. This flaw results in information leakage of the last byte of a confused field that overlaps with rec->tx_ready.

Critical Impact

This vulnerability enables local attackers with low privileges to leak sensitive kernel memory information through the TLS subsystem's improper list handling.

Affected Products

• Linux Kernel (all versions prior to the security patch)
• Systems utilizing kernel TLS offload functionality
• Linux-based operating systems and distributions running vulnerable kernel versions

Discovery Timeline

• 2023-03-27 - CVE-2023-1075 published to NVD
• 2025-02-24 - Last updated in NVD database

Technical Details for CVE-2023-1075

Vulnerability Analysis

This vulnerability is classified as a Type Confusion (CWE-843) combined with Information Exposure (CWE-200). The flaw resides in the TLS implementation within the Linux Kernel, specifically in the tls_is_tx_ready() function. The root cause is an improper check for list emptiness that allows access to a type confused entry in the list_head data structure.

When the function incorrectly evaluates the list state, it can access memory that belongs to a different data type than expected. This type confusion occurs because the confused field overlaps with rec->tx_ready, leading to the unintended disclosure of the last byte of kernel memory.

The vulnerability requires local access and low privileges to exploit, with no user interaction needed. While the confidentiality impact is limited to partial information disclosure, this type of memory leak could potentially be chained with other vulnerabilities for more significant attacks.

Root Cause

The vulnerability stems from an improper implementation of list emptiness checking in the tls_is_tx_ready() function. The function fails to correctly validate the list state before accessing list entries, resulting in type confusion when the list boundary conditions are not properly handled. This causes the function to read from an overlapping memory region where rec->tx_ready resides, leaking one byte of sensitive information.

Attack Vector

The attack vector is local, requiring an attacker to have authenticated access to the target system. The exploitation path involves:

1. An attacker with local, low-privileged access triggers the vulnerable code path in the TLS subsystem
2. The tls_is_tx_ready() function is called under specific conditions that trigger the improper list check
3. Due to type confusion, the function accesses memory belonging to the confused list_head entry
4. The last byte of the confused field overlapping with rec->tx_ready is leaked
5. The attacker can potentially collect this leaked information over multiple iterations

The vulnerability manifests within the kernel's TLS implementation during transmission readiness checks. For detailed technical analysis of the fix, see the Linux Kernel Commit.

Detection Methods for CVE-2023-1075

Indicators of Compromise

• Unusual patterns of TLS-related syscalls from low-privileged processes
• Anomalous access patterns to kernel TLS subsystem functions
• Processes attempting to read or manipulate TLS socket options repeatedly
• Unexpected memory access violations in TLS-related kernel code paths

Detection Strategies

• Monitor for unusual kernel TLS subsystem activity using kernel auditing tools (auditd)
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection and behavioral analysis
• Implement system call monitoring to detect suspicious patterns targeting TLS socket operations
• Use kernel tracing tools (ftrace, eBPF) to monitor tls_is_tx_ready() function calls

Monitoring Recommendations

• Enable kernel audit logging for network subsystem operations
• Implement real-time monitoring for TLS-related kernel functions using eBPF probes
• Deploy endpoint detection solutions capable of identifying kernel-level memory disclosure attempts
• Review system logs for evidence of repeated TLS socket manipulation attempts

How to Mitigate CVE-2023-1075

Immediate Actions Required

• Update the Linux Kernel to a patched version that includes commit ffe2a22562444720b05bdfeb999c03e810d84cbb
• Apply vendor-specific kernel patches from your Linux distribution's security repository
• Restrict local access to systems where TLS kernel offload is in use
• Monitor for any suspicious local activity targeting the TLS subsystem

Patch Information

The vulnerability has been addressed in the Linux Kernel through commit ffe2a22562444720b05bdfeb999c03e810d84cbb. This patch corrects the list emptiness check in the tls_is_tx_ready() function to prevent type confusion and subsequent information leakage. System administrators should update to a kernel version that includes this fix. For detailed patch information, refer to the Linux Kernel Commit.

Workarounds

• Limit local user access to systems running vulnerable kernel versions
• Disable TLS kernel offload if not required for operational purposes
• Implement strict access controls using SELinux or AppArmor policies
• Consider using user-space TLS implementations as an alternative until patching is complete

# Check current kernel version
uname -r

# Verify if TLS offload is enabled
cat /proc/sys/net/ipv4/tcp_fastopen

# Update kernel packages (Debian/Ubuntu)
sudo apt update && sudo apt upgrade linux-image-$(uname -r)

# Update kernel packages (RHEL/CentOS)
sudo yum update kernel