CVE-2024-0567: GnuTLS Distributed Trust DoS and Patch Guidance

A subtle bug in GnuTLS’s certificate-chain handling can be forced into crashing the library when presented with a specially crafted chain that uses distributed trust — a denial-of-service flaw tracked as CVE-2024-0567 that affected upstream releases before a patch was shipped and has since been addressed by maintainers and major distributions.

Background​

GnuTLS is an open-source TLS/SSL library widely embedded in Linux distributions, appliance software, and administration tooling. It provides the plumbing for TLS channels, certificate parsing and validation, and a suite of command-line utilities used by both administrators and services. In January 2024 the GnuTLS project and downstream vendors disclosed CVE-2024-0567 after maintainers and distributors observed that GnuTLS could incorrectly reject or mishandle a certificate chain that used distributed trust semantics; when that happened certain code paths could crash the process performing verification.
Major Linux distributors and security trackers flagged the issue and rolled out fixes: the vulnerability was broadly described as affecting upstream GnuTLS versions from 3.7.0 up to (but not including) 3.8.3, and the upstream remediation appears in releases that move the affected code out of the unsafe path. Distributors—including Red Hat, Ubuntu, SUSE, and others—published advisories and backported fixes into their gnutls packages.

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What the advisory actually says​

• The vulnerability is a denial-of-service (availability) issue: an unauthenticated remote client can trigger a crash during certificate chain validation.
• Affected upstream range: GnuTLS >= 3.7.0 and < 3.8.3. Upgrading to 3.8.3 or later is the recommended upstream fix; distributions have pushed equivalent packages to address the flaw.
• CVSS scoring varies by source (NVD lists a 7.5/High vector while some distributor trackers show slightly different vectors/scores depending on attack complexity assumptions). Operators should treat it as high priority for systems that expose certificate validation services to untrusted clients.

These short facts are the most important to keep in mind: the bug is not a cryptographic weakness that allows key theft or signature forgery, but it is a practical availability risk for services that accept and validate arbitrary certificate bundles or that run certificate-management tooling exposed to remote agents.

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Overview: distributed trust, cross-signed roots, and why this is tricky​

What is “distributed trust”?​

Distributed trust describes certificate chains where trust anchors are not strictly a single, linear chain from leaf to a single trusted root but are assembled from certificates that rely on cross-signatures or multiple trust paths. Real-world PKI is messy: intermediate certificates can be cross-signed, legacy roots can coexist with newer roots, and some systems accept alternate verification chains depending on available trust anchors. That complexity makes chain-building and sorting logic more subtle and brittle.

Why certificate-chain sorting matters​

A robust TLS stack must take an unordered set of certificates and build a valid chain from the end-entity certificate up to a trusted root. That requires sorting the certificates into parent–child relationships, detecting cross-signatures and loops, and deciding which certificates to prefer when multiple possible paths exist. Mistakes in this logic can cause infinite loops, assertion failures, or unexpected edge-case crashes when hostile inputs are encountered. In this case the problematic pathway occurred inside GnuTLS’s chain-sorting and validation routines.

The practical attack vector​

An attacker who can supply a crafted certificate chain to a validating endpoint — for example, via a management interface that accepts PEM bundles or a service that performs on-demand validation — can trigger the buggy sorting/verification code and crash the process. Because the exploit surface is certificate validation, any service that accepts remote certificate material for verification is at risk until patched.

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Technical deep dive: what goes wrong inside GnuTLS​

The available vendor and tracker write-ups describe the failure as arising when certificate chain validation encounters a distributed trust scenario that exercises a defective sort/compare path inside GnuTLS (the library’s internal sorting/ordering of certificate lists). This can lead to an assertion or similar abort inside the chain sorting function, which terminates the process using the library. Several vulnerability analyses reference an assertion in an internal routine (often summarized in trackers as gnutlssort_clist or equivalent), and downstream patches adjust sorting and validation to avoid the unsafe path.
Important clarifications about the technical nature:

• This is a crash/DoS — not remote code execution. The library’s behavior may cause the entire process to exit (or the thread to abort) depending on how the application links and handles assertions. The result is loss of availability for the affected service.
• The triggering input is a crafted certificate chain (PEM bundle) that relies on cross-signed roots or non-linear trust relationships. An ordinary, well-formed webserver certificate will not exercise this path in typical deployments.
• Because the attack depends on presenting certificate material to the verifier, the exposure is tied to services that accept certificates from untrusted peers — certificate enrollment endpoints, management interfaces (for example, Cockpit’s certificate operations), and tooling that verifies user-supplied PEM files.

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Who and what is affected​

Not every Linux system using GnuTLS is equally at risk. The real-world impact depends on whether the system:

• Uses an affected version of the GnuTLS library (upstream 3.7.0 through 3.8.2), and
• Runs software that accepts remote certificate material for validation — including administrative components like Cockpit (which the advisory explicitly mentions), certtool utilities that accept arbitrary bundles, or network-facing daemons that validate client-supplied certificate chains.

Major distributions published fixes and advisories indicating the package names and fixed release versions; for example, Ubuntu lists fixed packages in its gnutls28/gntls builds and marks the issue as fixed in the 3.8.3 package line, while Red Hat and SUSE issued errata referencing RHSA advisories and SUSE update notes. If you run distribution-provided gnutls packages, consult your distro’s security notices and update channels; if you use statically linked or vendor-bundled GnuTLS in appliances, you must review those artifacts separately.

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Detection: how to find affected systems and risky services​

Start with inventorying GnuTLS versions and services that perform certificate validation.

• Check packaged GnuTLS versions:
• RPM-based systems (RHEL/CentOS/Fedora/SUSE):
• rpm -q gnutls
• dnf list installed gnutls (or yum for older systems)
• Debian/Ubuntu:
• dpkg -l | grep gnutls
• apt-cache policy libgnutls30 gnutls28
• Alpine:
• apk info -v gnutls
• Look for services and tools that accept certificates:
• Cockpit, certtool, enrollment APIs, management consoles, or any web UI that takes PEM bundles.
• Use binary inspection for static linking:
• ldd /path/to/binary | grep gnutls
• strings /path/to/binary | grep -i gnutls
• Scan images and containers:
• For container fleets, use image scanning tools that check package versions (most scanners already flag CVE-2024-0567 against gnutls packages).

If a host is running an affected gnutls package and exposes a certificate-validation endpoint to untrusted clients, treat the system as high priority for patching or mitigation.

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Mitigation and remediation — immediate and medium-term steps​

• Patch: the single best corrective action is to upgrade GnuTLS to a fixed version. Upstream and distributors indicate 3.8.3 (or the equivalent patched package) as containing the remediation; distributions issued fixed packages and backports. Apply the vendor-supplied patch through your normal update channels (apt, dnf, zypper, apk, etc.).
• If immediate patching is not possible, apply temporary mitigations:
• Restrict access to certificate-validation endpoints to trusted management networks using firewall rules or access control lists. Where possible, bind management interfaces to loopback or internal networks only.
• Disable or remove services that accept remote certificate bundles until patched (for example, temporarily stop cockpit-certificate-ensure jobs or the cockpit service if it is not required).
• Use rate-limiting and process supervision (systemd restart limits, ulimit restrictions) to reduce the blast radius of repeated crash attempts and avoid full-system resource exhaustion.
• Consider running certificate-verification in a sandboxed helper process under supervision, so crashes do not terminate critical services; however, sandboxing is a design change and not a drop-in fix.
• Verify with vendor advisories: follow your distribution’s security notice for the exact package names and advisory IDs (Red Hat errata, Ubuntu packages, SUSE update announcements, etc.) and prefer the vendor backport on production systems.

Example distribution-specific remediation notes (representative):

• Ubuntu: packages in the gnutls28/gntls line were updated; check the Ubuntu security notice for the fixed package version and install it.
• Red Hat: RHSA advisories and errata labeled RHSA-2024:0533 (and subsequent advisories) include the fixed gnutls builds; use yum/dnf update to apply the errata.
• SUSE: SUSE published patches that list CVE-2024-0567 among fixed issues in updated gnutls packages.

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Hardening recommendations for administrators and DevOps​

• Treat certificate-validation endpoints like any other network-exposed input parser: minimize exposure, accept only authenticated/authorized peers where feasible, and place them behind a jump-host or VPN for management workflows.
• Limit process permissions and adopt the “least privilege” principle for admin tooling that uses GnuTLS. If the verifier does not need wide filesystem access, sandbox it.
• Add monitoring and alerting for unexpected crashes in processes that call gnutls: ensure core dumps are captured and alerting is in place so recurring crashes are detected quickly.
• Use image and artifact scanning that flags vulnerable gnutls packages and enforce updates in CI/CD pipelines. Many scanners and package-tracking feeds already include CVE-2024-0567 signatures; integrate these into automated patch workflows.

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For vendors and appliance maintainers: supply-chain considerations​

This CVE is a classic example of a library-level defect creating downstream effects across diverse products. Appliances and vendor-distributed images that embed GnuTLS (statically linked or bundled) must:

• Audit all shipped artifacts for bundled versions of gnutls and apply coordinated rebuilds where necessary. Static linking or frozen images will not benefit from OS package updates.
• Publish advisories and availability guidance promptly to customers, including explicit instructions for upgrading images or firmware.
• Consider providing a lightweight detection script/tool customers can run to confirm whether artifacts are vulnerable or already patched.

Distributors and vendors have already released package updates and advisories; administrators should prioritize devices and images that expose certificate validation to untrusted input.

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Risk assessment: how urgent is this?​

• Likelihood of exploitation: Moderate — an attacker must be able to submit certificate bundles to a validating endpoint. Public-facing services that accept PEM uploads or management interfaces exposed to the internet are higher risk.
• Impact if exploited: High for availability — a successful crash leads to a denial-of-service for the process and potentially for dependent services. There is no public evidence that the flaw enables remote code execution or key compromise.
• Exploit maturity: to date, public trackers show the issue as a DoS condition with theoretical exploitability; defenders should prioritize detection and patching but not treat this as a widespread RCE-level emergency. Still, the practical impact on management consoles and certificate enrollment flows can be significant.

Different sources assign slightly different CVSS values; NVD and several CNAs mark the vulnerability as high, while some distribution trackers offer lower severity ratings when they consider attack complexity and exposure. Organizations must interpret severity through their own threat model: any internet-accessible certificate-validation endpoint should be patched urgently.

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Practical checklist: what to do this week​

• Inventory: identify all systems with GnuTLS packages and services that validate certificates. (Use rpm/dpkg/apk queries and ldd to find static links.)
• Prioritize: flag any system with a public-facing management endpoint, certificate enrollment API, or admin console (e.g., Cockpit) for immediate remediation.
• Patch: apply the vendor-supplied package updates (or upgrade upstream GnuTLS to 3.8.3+) as soon as feasible. Confirm the package version post-update.
• Restrict: if patching will be delayed, firewall off management endpoints or bind them to internal networks only.
• Monitor: add alerts for repeated crashes or high restart rates of processes that use GnuTLS; capture logs and core dumps for post-mortem.
• Communicate: if you provide images or appliance firmware, notify customers about the issue and prepare patched artifacts or mitigation guidance.

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Why this matters beyond the immediate patch​

CVE-2024-0567 is symptomatic of two recurring realities in modern security:

• PKI complexity is real. Cross-signing, multiple trust anchors, and legacy roots create edge cases that make verification code brittle. Libraries must be rigorously fuzz-tested against crafted certificate material, and supply-chain consumers must expect regular certificate-parsing hardening work.
• Library bugs cascade. A defect in a widely used library like GnuTLS can affect dozens of services and appliances. The lesson for maintainers is to minimize the attack surface for certificate parsing, to bundle robust test suites, and to adopt layered defenses (network ACLs, process isolation) so a single library failure cannot easily take down critical infrastructure.

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Conclusion​

CVE-2024-0567 is a high-priority availability issue in GnuTLS’s certificate validation code when faced with distributed-trust chains. Upgrading to the fixed upstream release (3.8.3+) or installing distribution-supplied security updates is the correct, immediate response. Systems and appliances that accept certificate bundles from untrusted sources — particularly management consoles and enrollment APIs — should be treated as critical patch targets. Where patching cannot be immediate, administrators must restrict access, monitor for crashes, and adopt process-level hardening to limit blast radius. The fix is straightforward, but the event highlights enduring operational challenges around PKI complexity and the supply-chain reach of core cryptographic libraries.

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Source: MSRC Security Update Guide - Microsoft Security Response Center