CVE-2026-111814: 
Apache Traffic Server vulnerability analysis and mitigation

CVE-2026-111814 is a TLS session reuse vulnerability in Apache Traffic Server (ATS) that allows unauthenticated network attackers to bypass certificate-based authentication. The root cause is ATS's default outbound session-sharing policy, which can reuse a pooled TLS session authenticated with one client certificate for a transaction configured to present a different one. Affected versions include Apache Traffic Server 9.0.0 through 9.2.15, 10.0.0 through 10.1.4, and 10.2.0. The vulnerability was published on October 21, 2026, with patches available in versions 9.2.16, 10.1.5, and 10.2.1. It carries a CVSS v3.1 base score of 10.0 (Critical) and a CVSS v4.0 base score of 7.8 (High) (GitHub Advisory, Apache Mailing List).

The vulnerability is classified as CWE-295 (Improper Certificate Validation). ATS's default outbound session-sharing (connection pooling) mechanism fails to enforce that a reused TLS session presents the same client certificate as originally negotiated — meaning a pooled session authenticated with Client Certificate A can be reused for a transaction that should present Client Certificate B. This flaw requires no privileges, no user interaction, and no special attack preconditions, making it exploitable by any unauthenticated network attacker. No public proof-of-concept code has been identified at this time (GitHub Advisory, Apache Mailing List).

Successful exploitation allows an attacker to cause Apache Traffic Server to reuse TLS sessions with incorrect client certificates, effectively enabling impersonation of other clients and bypassing certificate-based mutual TLS (mTLS) authentication. The primary impact is on downstream/subsequent systems, where confidentiality and integrity are rated High — an attacker could access resources or submit requests as a different, potentially privileged client identity. Availability is not directly impacted, but the authentication bypass could facilitate unauthorized data access, privilege escalation, or lateral movement to backend services that rely on client certificate identity for access control (GitHub Advisory).

There is no evidence of public proof-of-concept exploit code or active in-the-wild exploitation at this time. No threat actor attribution has been reported. The EPSS score is 0.0, indicating a currently low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Despite the lack of active exploitation, the low attack complexity and absence of authentication requirements make this a high-priority patching target (GitHub Advisory).

Apache Software Foundation has released patched versions addressing this vulnerability: 9.2.16, 10.1.5, and 10.2.1. Users should upgrade to one of these versions as soon as possible. As an interim workaround where immediate patching is not feasible, administrators should review and reconfigure outbound session-sharing policies in ATS to enforce strict client certificate matching per transaction, preventing session reuse across different certificate identities (GitHub Advisory, Apache Mailing List).