---
id: "CVE-2026-111808"
kind: "vulnerability"
aliases: ["CVE-2026-111808"]
title: "Apache Traffic Server: malformed HTTP/2 frame exhausts origin worker pool"
severity: "high"
cvss: 8.6
epss: 0.00324
exploited: false
status: "open"
category: "runtime"
products: [{"name": "Apache Traffic Server", "fixed": ["9.2.16", "10.1.5", "10.2.1"], "affected": ">= 8.0.0, <= 8.1.11; >= 9.0.0, <= 9.2.15; >= 10.0.0, <= 10.1.4; 10.2.0", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["apache-traffic-server", "denial-of-service", "http2", "runtime", "self-hosted"]
not_affected_if: ["managed-hosting", "unaffected-versions"]
published_at: "2026-10-21T20:17:22+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-2026-111808", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-23T23:47:31+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-111808", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Apache Traffic Server: malformed HTTP/2 frame exhausts origin worker pool

A client can send a malformed padded HTTP/2 DATA frame to Apache Traffic Server. The padding underflows (CWE-191) and ATS allocates many backend worker threads on the HTTP/1.1 origin, exhausting its worker pool. No authentication is needed. Result is denial of service for legitimate users. Apache credits Khalilov Moe (LeetProtect) and the ASF. Part of a 15-CVE October 2026 release, and sibling CVE-2026-111805 is a similar h2 worker-pool issue.

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

## Affected

- vendor:Apache Traffic Server affected >= 8.0.0, <= 8.1.11; >= 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. You are affected on 8.0.0-8.1.11, 9.0.0-9.2.15, 10.0.0-10.1.4 or 10.2.0. Then see whether ATS accepts HTTP/2 from clients: look for h2 in the ALPN setting (proxy.config.ssl.client.alpn / records.yaml) and a TLS listener on your server ports. If clients can only use HTTP/1.1 the vendor does not say whether you are exposed (unconfirmed).

## Fix

Upgrade to 9.2.16, 10.1.5 or 10.2.1. 8.x has no fixed release, so move to 9.2.16 or later. The advisory lists no config workaround.

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-111808
- 2026-10-23T23:47:31+00:00 analyst — Read ATS Oct 2026 advisory and CVE record: CWE-191 padding underflow in HTTP/2 DATA frame, unauthenticated, network; CVSS 8.6 (3.1). Vendor page gives no workaround and no explicit statement that HTTP/2 must be on, but the trigger is an HTTP/2 frame so clients reaching ATS over h2 are the exposure. No public PoC or exploitation found; social search not done.
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-111808

## Documents

- [advisory] Apache Traffic Server October 2026 CVE Release https://trafficserver.apache.org/security-2026-10.html
- [describes] CVE Record: CVE-2026-111808 https://www.cve.org/CVERecord?id=CVE-2026-111808

## From the sources

Apache Traffic Server can be used to exhaust an HTTP/1.1 origin's worker pool via a malformed padded HTTP/2 DATA frame.



This issue affects Apache Traffic Server: from 8.0.0 through 8.1.11, 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.

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