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CVE-2025-14831: Death by a Thousand SANs: Analyzing CVE-2025-14831 in GnuTLS

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Death by a Thousand SANs: Analyzing CVE-2025-14831 in GnuTLS

Vulnerability ID: CVE-2025-14831
CVSS Score: 5.3
Published: 2026-02-09

A classic algorithmic complexity vulnerability hiding in the X.509 certificate verification logic of GnuTLS. By crafting a certificate with a pathological combination of Name Constraints and Subject Alternative Names (SANs), an attacker can force the library into an exponential validation loop. This results in severe CPU and memory exhaustion, effectively causing a Denial of Service (DoS) with a single TLS handshake.

TL;DR

GnuTLS versions prior to 3.8.12 choke on certificates with too many Name Constraints and SANs. The validation logic hits an O(N*M) complexity snag, allowing attackers to spike CPU usage and crash services via a malicious certificate. Patch by upgrading to 3.8.12.

Technical Details

  • CWE ID: CWE-407 (Inefficient Algorithmic Complexity)
  • CVSS v3.1: 5.3 (Medium)
  • Attack Vector: Network
  • Impact: Denial of Service (Resource Exhaustion)
  • EPSS Score: 0.00039 (Low probability)
  • Patch Date: 2026-02-09

Affected Systems

  • GnuTLS < 3.8.12
  • Red Hat Enterprise Linux 8/9/10
  • Ubuntu 22.04 / 24.04
  • Debian 12
  • Fedora 41/42/43
  • GnuTLS: < 3.8.12 (Fixed in: 3.8.12)

Code Analysis

Commit: acf67a4

Fix for CVE-2025-14831: Limit Name Constraints and SANs processing

Unspecified in context, involves loop optimizations and bounds checking.
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Exploit Details

  • Theoretical: Exploitation involves generating a certificate with thousands of SANs and Name Constraints.

Mitigation Strategies

  • Upgrade GnuTLS to version 3.8.12 or later.
  • Apply vendor-specific backported security patches immediately.
  • Implement rate limiting on incoming TLS connections to mitigate DoS impact.
  • Monitor CPU usage spikes correlated with TLS handshakes.

Remediation Steps:

  1. Identify vulnerable systems using gnutls-cli --version.
  2. Update package repositories: apt-get update or dnf check-update.
  3. Install the patch: apt-get install --only-upgrade libgnutls30 or equivalent.
  4. Restart all services depending on GnuTLS (e.g., Nginx, Exim, OpenVPN).
  5. Verify the fix by checking the version again.

References

Read the full report for CVE-2025-14831 on our website for more details including interactive diagrams and full exploit analysis.

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