CVE-2023-25076: Sniproxy Buffer Overflow RCE Vulnerability

CVE-2023-25076 Overview

CVE-2023-25076 is a buffer overflow vulnerability in SNIProxy, a transparent TLS proxy server that routes connections based on the hostname contained in the initial TLS Client Hello message. The vulnerability exists in the handling of wildcard backend hosts and can be exploited through specially crafted HTTP or TLS packets to achieve arbitrary code execution on affected systems.

Critical Impact

This vulnerability enables remote attackers to execute arbitrary code on systems running vulnerable SNIProxy versions without authentication or user interaction, potentially leading to complete system compromise.

Affected Products

• SNIProxy 0.6.0-2
• SNIProxy 0.6.1 (prior to patched version)
• SNIProxy master branch (commit: 822bb80df9b7b345cc9eba55df74a07b498819ba)

Discovery Timeline

• 2023-03-16 - SNIProxy 0.6.1 released with fix for buffer overflow
• 2023-03-30 - CVE-2023-25076 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-25076

Vulnerability Analysis

This buffer overflow vulnerability (CWE-120) affects SNIProxy's address module, specifically in the code path responsible for processing wildcard backend host configurations. When the proxy handles incoming HTTP or TLS connections, it parses the hostname from the request to determine the appropriate backend server routing. The vulnerable code fails to properly validate the length of input data before copying it into a fixed-size buffer, allowing an attacker to overflow the buffer boundaries.

The network-accessible nature of this vulnerability is particularly concerning for organizations using SNIProxy as a front-end proxy for TLS termination or traffic routing. An attacker can craft malicious packets that exploit this overflow condition, potentially overwriting adjacent memory and gaining control of program execution flow.

Root Cause

The root cause is a classic buffer overflow condition in the address handling module of SNIProxy. When processing wildcard backend host configurations, the software does not adequately check the bounds of input data before performing memory copy operations. This allows data to be written beyond the allocated buffer space, corrupting adjacent memory regions including potential return addresses or function pointers.

Attack Vector

The attack can be executed remotely over the network by sending specially crafted HTTP or TLS packets to an SNIProxy instance. The attacker does not require any authentication or privileges to exploit this vulnerability. The attack flow involves:

1. Attacker identifies an exposed SNIProxy service
2. Crafts a malicious HTTP or TLS packet with oversized hostname data
3. Sends the packet to the target SNIProxy server
4. The buffer overflow occurs during hostname processing
5. Attacker achieves arbitrary code execution with the privileges of the SNIProxy process

+2023-03-16  Dustin Lundquist <dustin@null-ptr.net>
+	0.6.1 Release
+
+	* Fix buffer overflow in address module
+	* Fix tests
+
 2018-12-05  Dustin Lundquist <dustin@null-ptr.net>
 	0.6.0 Release

Source: GitHub Commit Update

Detection Methods for CVE-2023-25076

Indicators of Compromise

• Unusual crash logs or core dumps from the SNIProxy process
• Abnormally long hostnames in TLS/HTTP request logs
• Unexpected child processes spawned by the SNIProxy service
• Network connections to suspicious external IP addresses originating from the proxy server

Detection Strategies

• Monitor SNIProxy process for unexpected terminations or restarts that may indicate exploitation attempts
• Implement network intrusion detection rules to identify packets with abnormally long hostnames in TLS Client Hello messages
• Deploy application-level logging to capture and analyze incoming connection metadata
• Use memory protection tools like Address Sanitizer during testing to detect buffer overflow conditions

Monitoring Recommendations

• Enable verbose logging on SNIProxy instances to capture connection details
• Set up alerts for SNIProxy service crashes or unexpected restarts
• Monitor system resource utilization for anomalies that may indicate post-exploitation activity
• Review network traffic patterns for connections with oversized TLS handshake data

How to Mitigate CVE-2023-25076

Immediate Actions Required

• Upgrade SNIProxy to version 0.6.1 or later immediately
• If immediate patching is not possible, consider temporarily disabling the SNIProxy service
• Implement network-level filtering to restrict access to SNIProxy from untrusted sources
• Review system logs for signs of exploitation attempts

Patch Information

The vulnerability has been addressed in SNIProxy version 0.6.1, released on March 16, 2023. The fix corrects the buffer overflow condition in the address module. The patch is available through the official GitHub Commit Update. Debian users can apply the fix through Debian Security Advisory DSA-5413 or the Debian LTS Security Advisory.

For detailed technical information about the vulnerability, refer to the Talos Intelligence Vulnerability Report.

Workarounds

• Restrict network access to SNIProxy using firewall rules to only allow trusted source IP addresses
• Deploy SNIProxy behind a web application firewall (WAF) that can filter malformed requests
• Consider using an alternative proxy solution until patching can be completed
• Implement network segmentation to limit the blast radius if exploitation occurs

# Version update in configure.ac showing the fix
AC_PREREQ([2.60])
-AC_INIT([sniproxy], [0.6.0])
+AC_INIT([sniproxy], [0.6.1])
AC_CONFIG_SRCDIR([src/sniproxy.c])
AC_CONFIG_MACRO_DIR([m4])
AM_INIT_AUTOMAKE([subdir-objects])

Source: GitHub Commit Update