External risk intelligence

Apache Tomcat CRL Configuration Error Allows Sensitive Data Disclosure

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-53434

Apache Tomcat is a widely deployed web server and servlet container that is commonly positioned as an internet-facing web application server or edge service to process incoming network requests.

Apache Tomcat

9.0.83 to before 9.0.11910.1.0 to before 10.1.5611.0.0 to before 11.0.23

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in Apache Tomcat, a widely used web server software, which could allow for the unauthorized disclosure and modification of data. This issue arises from how the software handles specific error conditions when configured for certain network connections. The potential impact at a high level could affect the integrity and confidentiality of information processed by affected systems.

Error handling flaw in web server software.
Critical flaw could impact data confidentiality and integrity.
Confirm relevance and assess potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by configuring Certificate Revocation Lists (CRLs) for a FFM-based connector within an affected Apache Tomcat server. This misconfiguration allows the server to fail to detect an error condition, potentially leading to unauthorized access to sensitive information and modification of data.

No authentication or privileges required.
Configuring CRLs for FFM connector.
Unauthorized access and data modification.

Live Threat

Current exploitation, exposure, and threat context

When configured with CRLs for an FFM-based connector, Apache Tomcat could encounter an error condition that is not handled. This may lead to an unauthenticated attacker potentially affecting service integrity and confidentiality, when supported by the advisory's configuration.

Unhandled error conditions.
Network access to connector configuration.
Service integrity and confidentiality.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Apache Tomcat vulnerability requires immediate attention from teams managing web application infrastructure. System owners should prioritize identifying all instances of the affected Tomcat versions, assessing their exposure, and confirming business criticality. This will enable a risk-based remediation plan, coordinating with relevant teams to address the vulnerability.

Platform or infrastructure teams own this.
Verify external reachability and business criticality.
Plan updates during the next maintenance window.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Apache Tomcat?

Apache Tomcat is an open-source web server and servlet container widely used to host Java-based web applications. It acts as the engine that processes incoming network requests and runs server-side code, serving as the bridge between web traffic and back-end application logic.

What does CWE-390 mean for CVE-2026-53434?

CWE-390, or Detection of Error Condition Without Action, describes a software flaw where the program encounters an error but fails to notice it or react appropriately. In this CVE, Tomcat proceeds as if an operation succeeded even when an error occurs during CRL processing, leaving the system in an insecure state.

How is this vulnerability triggered?

The issue is triggered specifically when a system is configured to use Certificate Revocation Lists (CRLs) for a Foreign Function & Memory (FFM) based connector. If CRLs are not configured for this specific connector type, the vulnerability is not triggered.

Do I need to worry about this if my server is internal?

Halo Surface Signal notes that because this component is often used as an internet-facing edge service, the risk is higher for those deployments. While internal services are also affected, the lack of authentication required to reach the vulnerable connector makes internet-accessible instances a primary concern for data integrity.

How do I address this Tomcat issue?

Start by identifying all instances of Tomcat within your infrastructure and checking their versions against the affected ranges. Prioritize updating these servers to the patched versions—11.0.23, 10.1.56, or 9.0.119—according to your organization's standard maintenance and deployment procedures.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.