---
id: "CVE-2026-110499"
kind: "vulnerability"
aliases: ["CVE-2026-110499"]
title: "Bandit: HTTP/2 client can grow server memory and CPU without limit"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["bandit", "elixir", "package", "phoenix", "self-hosted"]
not_affected_if: ["bandit-1.14.0-or-later", "http1-only", "http2-terminated-at-proxy"]
published_at: "2026-10-26T14:16:26+00:00"
first_seen_at: "2026-10-26T14:30:36+00:00"
updated_at: "2026-10-26T14:32:12+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110499", "first_seen_at": "2026-10-26T14:30:36+00:00"}]
---

# Bandit: HTTP/2 client can grow server memory and CPU without limit

Bandit, an Elixir HTTP server, resizes its HPACK header table to whatever size a client requests in SETTINGS, up to about 4 GB, and never evicts entries. An unauthenticated remote client can make each connection consume unbounded memory and CPU, slowing or exhausting the server.

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

## How to check

- Check the bandit version in `mix.lock` or `mix deps` output and confirm whether it is below `1.14.0`
- Confirm the application serves HTTP/2 by checking for `http_2` or `:http_2` options in the endpoint configuration

## Fix

- Upgrade the `bandit` dependency to `1.14.0` or later and redeploy
- Put a reverse proxy or load balancer with HTTP/2 connection limits in front of the service until the upgrade is applied

## Timeline

- 2026-10-26T14:30:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-110499

## From the sources

Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to grow per-connection memory and CPU cost without bound via a large SETTINGS_HEADER_TABLE_SIZE. Bandit resizes its HPACK encoder table to whatever size the client advertises, up to 2^32-1 bytes, and indexes response headers into it. Because responses carry distinct values such as date or content-length, nothing is evicted and the table grows with every response for the life of the connection, while each lookup scans it linearly.

The SETTINGS handling in Bandit.HTTP2.Connection (lib/bandit/http2/connection.ex) passes remote_settings.header_table_size to HPAX.resize/2 with no server-side cap, and encode_headers encodes every response header as :store. Serving N responses on one connection therefore costs O(N²) CPU in the connection process.

This issue affects bandit: from 0.3.6 before 1.14.0.

---

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