CVE-2026-1584: GnuTLS DoS Vulnerability

CVE-2026-1584 Overview

A critical vulnerability has been identified in GnuTLS, a widely-used open-source TLS library. This flaw allows a remote, unauthenticated attacker to trigger a NULL pointer dereference by sending a specially crafted ClientHello message with an invalid Pre-Shared Key (PSK) binder value during the TLS handshake. Successful exploitation results in a server crash, causing a remote Denial of Service (DoS) condition.

Critical Impact

Remote attackers can crash TLS-enabled services without authentication, potentially disrupting critical infrastructure and communications relying on GnuTLS for secure connections.

Affected Products

• GnuTLS library (versions with PSK support enabled)
• Applications and services using vulnerable GnuTLS versions for TLS handshake processing
• Linux distributions and systems shipping affected GnuTLS packages

Discovery Timeline

• 2026-04-09 - CVE-2026-1584 published to NVD
• 2026-04-09 - Last updated in NVD database

Technical Details for CVE-2026-1584

Vulnerability Analysis

This vulnerability (CWE-476: NULL Pointer Dereference) exists in GnuTLS's handling of Pre-Shared Key (PSK) binder values during the TLS 1.3 handshake process. When a client initiates a TLS connection and includes PSK extensions in the ClientHello message, the server must validate the binder value to authenticate the pre-shared key. The flaw occurs when the GnuTLS server processes a malformed PSK binder that leads to dereferencing a NULL pointer, causing the application to crash immediately.

The vulnerability is particularly concerning because it can be triggered remotely without any authentication, and the attack requires only network access to the target TLS service. No user interaction is needed, and the attacker does not require any privileges on the target system.

Root Cause

The root cause lies in insufficient validation of PSK binder values during the TLS handshake. When processing ClientHello messages containing Pre-Shared Key extensions, GnuTLS fails to properly check for NULL pointer conditions before dereferencing memory associated with the binder validation logic. This improper input validation allows a crafted malicious binder value to bypass expected checks and trigger the NULL pointer dereference.

Attack Vector

The attack is executed over the network by sending a specially crafted ClientHello message to any TLS server using the vulnerable GnuTLS library. The attacker constructs a malformed PSK extension with an invalid binder value designed to exploit the NULL pointer dereference condition. When the server attempts to process and validate this binder, it dereferences a NULL pointer, resulting in a segmentation fault and immediate service crash.

The exploitation does not require any prior authentication or session establishment—simply initiating a malformed TLS handshake is sufficient to trigger the vulnerability. This makes it trivial for attackers to repeatedly crash services, causing sustained denial of service conditions.

Detection Methods for CVE-2026-1584

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using GnuTLS during TLS handshake operations
• Service availability issues correlated with incoming TLS connection attempts
• Core dumps showing NULL pointer dereference in GnuTLS PSK binder validation functions
• Anomalous ClientHello messages with malformed PSK extensions in network traffic logs

Detection Strategies

• Monitor application logs for segmentation faults or crashes occurring during TLS handshake initialization
• Deploy network intrusion detection signatures to identify malformed TLS ClientHello messages with anomalous PSK binder values
• Implement crash dump analysis to identify NULL pointer dereferences in GnuTLS library functions
• Configure endpoint detection to alert on repeated service restarts or crashes of TLS-enabled applications

Monitoring Recommendations

• Enable verbose logging for TLS handshake events in applications using GnuTLS
• Deploy network-level monitoring to detect unusual patterns of failed TLS handshakes from single sources
• Monitor system health metrics for unexpected service crashes and automatic restarts
• Set up alerts for core dump generation in production TLS services

How to Mitigate CVE-2026-1584

Immediate Actions Required

• Review and update GnuTLS packages when security patches become available from your distribution vendor
• Consider implementing rate limiting on TLS connection attempts to reduce DoS impact
• Monitor Red Hat CVE-2026-1584 Advisory for official patch releases
• Review Red Hat Bug Report #2435258 for additional technical details and mitigation guidance

Patch Information

Security patches should be applied as soon as they become available from GnuTLS maintainers or distribution vendors. Organizations should monitor the official Red Hat security advisory and GnuTLS project announcements for patch availability. When patches are released, prioritize updating all systems running TLS services that rely on GnuTLS for cryptographic operations.

Workarounds

• If PSK functionality is not required, consider disabling PSK cipher suites in GnuTLS configuration to reduce attack surface
• Implement network-level filtering to block suspicious TLS handshake patterns at perimeter defenses
• Deploy Web Application Firewalls (WAF) or TLS-aware proxies that can inspect and filter malformed ClientHello messages
• Consider using alternative TLS libraries for critical services until a patch is available, if operationally feasible

# Example: Check GnuTLS version on your system
gnutls-cli --version

# Example: Monitor for crashes in GnuTLS-dependent services
journalctl -u your-tls-service --since "1 hour ago" | grep -i "segfault\|crash\|NULL"