CVE-2026-86247 in Tomcat Native
Summary
by MITRE • 09/23/2026
Race condition within a thread vulnerability in Apache Tomcat Native allowed client certificate verification requirements to be down-graded for some configurations.
This issue affects Apache Tomcat Native: from 2.0.0 through 2.0.15, from 1.3.0 through 1.3.8. Unsupported versions may also be affected.
Users are recommended to upgrade to version 2.0.16 or 1.3.9, which fixes the issue.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in Apache Tomcat Native represents a critical race condition within its thread management logic that directly compromises the integrity of client certificate verification processes. This flaw allows an attacker to potentially downgrade security requirements for specific configurations by exploiting timing windows during the initialization or validation phases of SSL/TLS connections. The root cause lies in how multiple threads interact with shared state variables related to OpenSSL context settings, specifically when handling mutual authentication scenarios where both server and client certificates are required. If a thread modifies configuration parameters while another is actively verifying credentials, the verification logic may proceed using outdated or incomplete security constraints, effectively bypassing strict certificate validation rules that were intended by the administrator.
This race condition primarily impacts environments configured for two-way SSL or mutual TLS authentication, where robust identity verification of connecting clients is essential for access control and data integrity. By exploiting this timing vulnerability, a malicious actor could potentially authenticate as an unauthorized client without possessing valid credentials, provided they can manipulate network latency or connection patterns to widen the race window. The operational impact includes unauthorized access to protected resources, potential data exfiltration, and a complete breakdown of trust boundaries established by PKI infrastructure. Since Apache Tomcat Native serves as the bridge between the Java-based Tomcat application server and the underlying OpenSSL library, any compromise in its native code execution environment undermines the entire security posture of applications relying on it for encrypted communications.
The affected versions span from 2.0.0 through 2.0.15 and from 1.3.0 through 1.3.8, indicating that this issue has persisted across multiple minor releases due to insufficient synchronization mechanisms in the native codebase. Unsupported versions may also be susceptible if they share similar architectural patterns regarding thread-safe handling of SSL contexts. The vulnerability aligns with CWE-362, which describes concurrent execution race conditions leading to unintended state changes, and maps closely to ATT&CK technique T1078, specifically valid accounts or authentication bypass scenarios where identity verification is subverted through technical exploitation rather than credential theft.
To mitigate this risk, organizations must upgrade Apache Tomcat Native to version 2.0.16 or 1.3.9 immediately upon availability in their deployment pipelines. These patched versions implement proper locking mechanisms and atomic operations to ensure that configuration changes do not interfere with ongoing verification processes. Additionally, administrators should review current SSL/TLS configurations to enforce strict cipher suites and certificate validation policies that are less susceptible to timing-based attacks. Regular security audits and penetration testing focusing on authentication flows can help identify residual risks in legacy systems where upgrading may not be immediately feasible. Monitoring for anomalous connection patterns or failed authentication attempts from unexpected sources provides an additional layer of defense against exploitation attempts targeting this specific race condition.