CVE-2026-0719: libsoup Buffer Overflow Vulnerability

CVE-2026-0719 Overview

A stack-based buffer overflow vulnerability has been identified in libsoup's NTLM (NT LAN Manager) authentication module. When NTLM authentication is enabled, a local attacker can exploit this vulnerability in the md4sum() function to overwrite adjacent memory regions. Successful exploitation may result in arbitrary code execution with the privileges of the affected application, potentially leading to complete system compromise.

Critical Impact

Local attackers can achieve arbitrary code execution by exploiting the stack-based buffer overflow in libsoup's NTLM authentication, potentially gaining full control over systems using vulnerable versions of the library.

Affected Products

• libsoup library (versions with NTLM authentication enabled)
• Applications utilizing libsoup for HTTP communications with NTLM authentication
• GNOME-based systems and distributions using vulnerable libsoup versions

Discovery Timeline

• 2026-01-08 - CVE-2026-0719 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2026-0719

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), which occurs when a buffer allocated on the stack is overwritten beyond its intended boundary. The flaw resides specifically in the md4sum() function within libsoup's NTLM authentication module.

The vulnerability requires local access to exploit, meaning an attacker must have some level of access to the target system. Once positioned, the attacker can craft malicious input that triggers the buffer overflow condition within the NTLM authentication process. The overflow allows writing beyond the allocated stack buffer, overwriting adjacent memory including potentially critical data such as return addresses and saved registers.

The impact is significant as successful exploitation grants the attacker code execution privileges equivalent to those of the vulnerable application. Since libsoup is a widely-used HTTP client/server library in the GNOME ecosystem, applications processing NTLM authentication through this library become potential attack vectors.

Root Cause

The root cause lies in insufficient bounds checking within the md4sum() function during NTLM authentication processing. The function fails to properly validate the size of input data before copying it into a fixed-size stack buffer, allowing attackers to supply oversized input that overflows the buffer boundary. This classic memory safety issue enables stack corruption and potential control flow hijacking.

Attack Vector

The attack vector is local, requiring the attacker to have existing access to the target system. Exploitation involves:

1. Identifying an application using libsoup with NTLM authentication enabled
2. Crafting malicious NTLM authentication data designed to overflow the stack buffer in md4sum()
3. Overwriting stack memory to redirect execution flow
4. Achieving arbitrary code execution with the application's privileges

The vulnerability can be triggered during NTLM authentication exchanges where the malformed data is processed by the vulnerable md4sum() function. Technical details and tracking information are available through the GNOME Libsoup Issue #477 and Red Hat Bugzilla Issue #2427906.

Detection Methods for CVE-2026-0719

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications utilizing libsoup with NTLM authentication
• Anomalous memory access patterns or stack corruption indicators in application logs
• Unusual process behavior or unexpected child process spawning from libsoup-dependent applications
• Evidence of code execution attempts following NTLM authentication events

Detection Strategies

• Monitor system and application logs for crashes related to libsoup or NTLM authentication failures
• Deploy memory corruption detection tools (e.g., AddressSanitizer, Valgrind) during testing to identify exploitation attempts
• Implement runtime application self-protection (RASP) solutions to detect buffer overflow attempts
• Use SentinelOne's behavioral AI to identify anomalous process execution patterns indicative of exploitation

Monitoring Recommendations

• Enable detailed logging for applications using libsoup with NTLM authentication enabled
• Configure crash dump collection and analysis for applications dependent on libsoup
• Monitor for unusual network authentication patterns or repeated failed NTLM authentication attempts
• Implement endpoint detection and response (EDR) rules to flag suspicious memory access in libsoup-dependent processes

How to Mitigate CVE-2026-0719

Immediate Actions Required

• Identify all systems and applications using libsoup with NTLM authentication enabled
• Disable NTLM authentication in libsoup if not strictly required for operations
• Apply vendor-provided patches as soon as they become available
• Implement network segmentation to limit exposure of vulnerable systems
• Monitor the Red Hat CVE-2026-0719 Advisory for patch availability

Patch Information

Organizations should monitor official distribution channels for security updates addressing this vulnerability. Key resources include:

• Red Hat CVE-2026-0719 Advisory for Red Hat-based systems
• GNOME Libsoup Issue #477 for upstream patch information
• Red Hat Bugzilla Issue #2427906 for detailed tracking

Apply updates through your distribution's package manager as patches become available.

Workarounds

• Disable NTLM authentication in libsoup configuration where alternative authentication methods are viable
• Use alternative authentication mechanisms such as Kerberos or Basic authentication over TLS
• Implement application-level sandboxing to limit the impact of potential exploitation
• Deploy network-level controls to restrict access to systems running vulnerable applications

# Example: Check for libsoup installation and version
rpm -qa | grep libsoup
dpkg -l | grep libsoup

# Check if NTLM authentication is in use by applications
grep -r "ntlm" /etc/ 2>/dev/null
ldd /path/to/application | grep soup