---
id: "CVE-2026-110353"
kind: "vulnerability"
aliases: ["CVE-2026-110353"]
title: "HAProxy: truncated HTTP/2 PING frame spins worker threads, causing denial of service"
severity: "high"
cvss: 7.5
epss: 0.00684
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["haproxy", "http2", "load-balancer", "runtime", "self-hosted"]
not_affected_if: ["default-config"]
published_at: "2026-10-22T03:16:31+00:00"
first_seen_at: "2026-10-23T21:57:30+00:00"
updated_at: "2026-10-25T03:16:14+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110353", "first_seen_at": "2026-10-23T21:57:30+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-110353", "first_seen_at": "2026-10-24T07:15:52+00:00"}]
---

# HAProxy: truncated HTTP/2 PING frame spins worker threads, causing denial of service

HAProxy 3.2 before 3.4.6 does not check for short reads in its HTTP/2 PING frame handler, so a truncated PING leaves data unconsumed and the multiplexer tasklet spins. An unauthenticated remote attacker opening many such connections can exhaust worker-thread CPU and deny service.

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

## How to check

- Run `haproxy -v` and check whether the version is 3.2.x below `3.4.6`.
- Check whether HTTP/2 is enabled on a frontend (`proto h2` or `alpn h2` in the `bind` line of `haproxy.cfg`).

## Fix

- Upgrade HAProxy to `3.4.6` or later.
- Until upgraded, the sources do not name a configuration workaround: unknown.

## Timeline

- 2026-10-23T21:57:30+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-110353
- 2026-10-24T07:15:52+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-110353

## From the sources

HAProxy 3.2 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (worker-thread CPU exhaustion) via a truncated HTTP/2 PING frame. h2c_handle_ping in src/mux_h2.c does not check for a short read, unlike the other H2 frame handlers. Because the incomplete frame cannot be processed, its data is never consumed, and the H2 multiplexer tasklet is repeatedly woken by that pending data without making progress. The CPU spins until timeout http-request closes the connection, and an attacker opening many such connections can sustain high CPU usage.

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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_