Critical GnuTLS vulnerabilities CVE-2025-32988, CVE-2025-32990, & CVE-2025-6395 exposed. Learn how to patch your Ubuntu 18.04, 20.04 systems to prevent denial-of-service attacks & arbitrary code execution. Secure your servers now.
Executive Summary: Urgent Action Needed
Have you updated your Ubuntu servers today? A set of critical security vulnerabilities has been discovered in GnuTLS, the fundamental GNU Transport Layer Security library that encrypts communications for countless applications and services on Linux systems.
These flaws, tagged as CVE-2025-32988, CVE-2025-32990, and CVE-2025-6395, pose a severe risk, potentially allowing remote attackers to crash systems in a denial-of-service (DoS) attack or, even worse, execute arbitrary code to gain control.
This article provides a comprehensive breakdown of these GnuTLS security issues, the affected Ubuntu versions, and the crucial steps required to mitigate these cyber threats immediately.
Detailed Analysis of the GnuTLS Security Flaws
The Ubuntu security team, in conjunction with global researchers, identified several distinct weaknesses within the GnuTLS cryptographic library. Understanding the technical specifics of each vulnerability is key to appreciating the risk level and the necessity of a prompt patch management routine.
1. CVE-2025-32988: Subject Alternative Name (SAN) Parsing Overflow
Nature of the Flaw: This vulnerability involves an incorrect handling of exporting Subject Alternative Name (SAN) entries that contain an
otherNamefield. SANs are a critical component of X.509 certificates, used to specify additional hostnames a certificate is valid for.
Potential Impact: A remote attacker could craft a malicious certificate or traffic that, when processed by a vulnerable GnuTLS instance, triggers a buffer overflow or improper memory access. This could lead to a application crash, causing a denial of service, or potentially allow the attacker to execute their own code on the target system.
Affected Systems: This issue only affected Ubuntu 18.04 LTS (Bionic Beaver) and Ubuntu 20.04 LTS (Focal Fossa). Newer LTS releases like 22.04 (Jammy Jellyfish) and 24.04 (Noble Numbat) are not impacted.
2. CVE-2025-32990 & CVE-2025-6395: Certtool Template File Vulnerabilities
Nature of the Flaw: These two related vulnerabilities exist within the
certtoolutility, a command-line tool for generating and managing certificates. The flaws revolve around the incorrect parsing of certain template files used bycerttool.
Potential Impact: An attacker with the ability to provide a maliciously crafted template file to
certtoolcould exploit a memory corruption bug. Similar to CVE-2025-32988, this could result in a crash of the utility (Denial-of-Service) or arbitrary code execution within the context of the user runningcerttool.
Affected Systems: CVE-2025-32990 affects a broader range of systems. CVE-2025-6395 specifically only affected Ubuntu 20.04 LTS.
Mitigation and Patch Instructions: How to Secure Your System
The primary and most critical mitigation strategy for these vulnerabilities is to immediately apply the available security patches. The Ubuntu security team has released updated packages that resolve these issues.
Update Instructions
In most cases, a standard system update will make all the necessary changes. You can achieve this by running the following commands in your terminal:
sudo apt update sudo apt upgrade
This will fetch and install the latest security patches for all packages, including GnuTLS. For precise version control, the following package versions contain the fixes:
| Ubuntu Release | Package Name | Patched Version |
|---|---|---|
| 20.04 LTS (Focal Fossa) | libgnutls30 | 3.6.13-2ubuntu1.12+esm1 |
| 18.04 LTS (Bionic Beaver) | libgnutls30 | 3.5.18-1ubuntu1.6+esm2 |
| 16.04 LTS (Xenial Xerus) | libgnutls30 | 3.4.10-4ubuntu1.9+esm2 |
After updating, it is highly recommended to restart any services that actively use GnuTLS (e.g., web servers like Apache or Nginx, email servers, VPN endpoints) or simply reboot the entire system to ensure all loaded libraries are refreshed.
Beyond the Patch: Reducing Your Security Exposure
While patching is reactive, a proactive security posture is essential in modern IT infrastructure. For organizations relying on long-term support releases, maintaining security over a decade can be challenging.
Ubuntu Pro, a paid subscription service, provides expanded security coverage for the Main and Universe repositories for up to ten years, covering over 25,000 packages. This is invaluable for compliance-driven environments that cannot upgrade frequently. Best of all, it's free for personal use on up to five machines.
Action: Get Ubuntu Pro to extend your security maintenance and protect against vulnerabilities in a wider range of software.
The Bigger Picture: Why TLS Library Security is Non-Negotiable
GnuTLS is not just another package; it is a core dependency for secure communication. A vulnerability in a TLS library is among the most critical types of security bugs, as it undermines the very trust and encryption that modern internet communication relies on.
This incident underscores a constant trend in cybersecurity: the open-source software supply chain is a prime target. The rapid identification and patching of these flaws by the GnuTLS maintainers and Ubuntu security team demonstrate the strength of the collaborative open-source security model.
Frequently Asked Questions (FAQ)
Q1: I’m running Ubuntu 22.04 or 24.04. Am I vulnerable?
A: Based on the Ubuntu security notice USN-7742-1, these specific vulnerabilities do not affect Ubuntu 22.04 LTS (Jammy Jellyfish) or 24.04 LTS (Noble Numbat). However, maintaining regular updates is always a critical best practice.
Q2: What is the difference between a DoS and Arbitrary Code Execution?
A: A Denial-of-Service (DoS) attack crashes the service, making it unavailable. Arbitrary Code Execution is far more severe, as it allows an attacker to run any command or program on your server, potentially leading to full system compromise, data theft, or using your system as a foothold for further attacks.
Q3: Do I need to restart my server after updating?
A: While the package update replaces the library files on disk, services already running in memory will still be using the old, vulnerable version. A restart of those specific services or a full system reboot is necessary to complete the mitigation.
Q4: Where can I find more technical details about these CVEs?
A: You can reference the official CVE pages from MITRE or the National Vulnerability Database (NVD) by searching for the CVE identifiers: CVE-2025-32988, CVE-2025-32990, and CVE-2025-6395.
Conclusion: Prioritize This Update Immediately
The discovery of these GnuTLS vulnerabilities serves as a stark reminder of the importance of vigilant system maintenance. The potential for remote code execution elevates this from a mere inconvenience to a critical threat that must be addressed with urgency.
By applying the provided security patches promptly, system administrators can protect their infrastructure from potential exploits targeting these vulnerabilities. Ensure your systems are updated, consider a robust security strategy like Ubuntu Pro for long-term coverage, and maintain the integrity of your encrypted communications
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