---
id: "CVE-2026-111814"
kind: "vulnerability"
aliases: ["CVE-2026-111814"]
title: "Apache Traffic Server: pooled TLS sessions reused across different client certificates"
severity: "critical"
cvss: 10.0
epss: 0.00172
exploited: false
status: "open"
category: "infrastructure"
products: [{"name": "Apache Traffic Server", "fixed": ["9.2.16", "10.1.5", "10.2.1"], "affected": ">= 9.0.0, <= 9.2.15; >= 10.0.0, <= 10.1.4; 10.2.0", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["apache-traffic-server", "client-certificates", "infrastructure", "mtls", "outbound-tls", "reverse-proxy", "self-hosted"]
not_affected_if: ["no-origin-client-certs", "no-outbound-client-certificates", "not-using-ats"]
published_at: "2026-10-21T20:17:23+00:00"
first_seen_at: "2026-10-23T21:57:29+00:00"
updated_at: "2026-10-24T13:15:54+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-111814", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-23T22:49:43+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-111814", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Apache Traffic Server: pooled TLS sessions reused across different client certificates

Apache Traffic Server's default outbound session-sharing policy can reuse a pooled TLS session that was authenticated with one client certificate for a transaction meant to present a different certificate. An attacker can therefore reach upstream servers under another client's identity.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Apache Traffic Server affected >= 9.0.0, <= 9.2.15; >= 10.0.0, <= 10.1.4; 10.2.0 fixed 9.2.16, 10.1.5, 10.2.1

## How to check

Run traffic_server -V to get the version. Exposed if it is 9.0.0-9.2.15, 10.0.0-10.1.4 or 10.2.0 AND ATS makes TLS connections to origins that need client certificates (mTLS), with different certificates for different transactions or remaps. Check proxy.config.http.server_session_sharing.match in records.yaml or records.config. The default omits the certificate mask (MASK_CERT), so the default is affected. If you never present client certificates to origins, you are not exposed.

## Fix

Upgrade to 9.2.16, 10.1.5 or 10.2.1. The advisory names no workaround; unverified suggestion: set server_session_sharing.match so it includes the cert mask, or turn off origin session sharing.

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-111814
- 2026-10-23T22:49:43+00:00 analyst — Read Apache ATS Oct 2026 advisory (primary): default server_session_sharing.match omits MASK_CERT; fixed 9.2.16/10.1.5/10.2.1; reporter Craig Taylor. Apache rates Important; CVSS 3.1 is 10.0, v4.0 is 7.8. No exploitation or PoC reported (StackRef bulletin). No social posts searched. Advisory gives no config snippet; how_to_check is inferred from the setting name.
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-111814

## Documents

- [advisory] Apache Traffic Server October 2026 CVE Release https://trafficserver.apache.org/security-2026-10.html
- [mentions] The Whistle: mTLS bypasses in Traffic Server and Traefik https://whistle.stackref.com/post/2026-10-22-cve-bulletin-ats-traefik-trust/

## From the sources

Apache Traffic Server's default outbound session-sharing policy can reuse a pooled TLS session authenticated with one client certificate for a transaction configured to present a different one.



This issue affects Apache Traffic Server: from 9.0.0 through 9.2.15, from 10.0.0 through 10.1.4, 10.2.0.



Users are recommended to upgrade to version 9.2.16, 10.1.5, or 10.2.1, which fix the issue.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_