---
id: CVE-2026-108529
title: >-
  SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked
  streams in Bandit
summary: >-
  Inefficient Algorithmic Complexity vulnerability in the HTTP/2 implementation
  of mtrudel bandit allows an unauthenticated remote attacker to exhaust server
  CPU via small SETTINGS or connection-level WINDOW_UPDATE frames. The attacker
  ope…
severity: high
cvss: 8.7
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cvssSource: cna
cwe:
  - CWE-407
vendor: mtrudel
product: bandit
affected:
  - bandit >= 0.3.4 < 1.14.0
  - >-
    mtrudel/bandit >= 6feadb31189d18b7dcda6c663112cd3bbaf63a46 <
    220b9dfd27f9a21305be2afc75cbe585ddc24e7a
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-26T15:01:20.277475Z'
published: '2026-10-26'
updated: '2026-10-26'
sourceUpdated: '2026-10-26T15:35:50.781Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-108529'
references:
  - url: 'https://github.com/mtrudel/bandit/security/advisories/GHSA-j363-h72p-296m'
    label: >-
      SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over
      blocked streams
  - url: 'https://cna.erlef.org/cves/CVE-2026-108529.html'
    label: EEF CNA record for CVE-2026-108529
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-108529'
    label: OSV record EEF-CVE-2026-108529
  - url: >-
      https://github.com/mtrudel/bandit/commit/6feadb31189d18b7dcda6c663112cd3bbaf63a46
    label: Introducing commit 6feadb3 in mtrudel/bandit
  - url: >-
      https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a
    label: Fix commit 220b9df in mtrudel/bandit
tags:
  - cve.org
ingestedAt: '2026-10-26T14:27:31.819Z'
---

## Overview

Inefficient Algorithmic Complexity vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to exhaust server CPU via small SETTINGS or connection-level WINDOW_UPDATE frames. The attacker opens thousands of streams whose responses block on the connection send window, then sends cheap frames that each make the server walk the whole queue of blocked sends. In the reporter's run, with 3,000 blocked streams a single 9-byte SETTINGS frame took 133 ms to process.

do_pending_sends/2 in lib/bandit/http2/connection.ex retries every queued send and, before each retry, removes that entry from the queue with List.delete/2, so one frame costs O(n²) list operations for n blocked streams. max_concurrent_streams defaults to :infinity, so the attacker chooses n.

This issue affects bandit: from 0.3.4 before 1.14.0.

## Affected

- `bandit >= 0.3.4 < 1.14.0`
- `mtrudel/bandit >= 6feadb31189d18b7dcda6c663112cd3bbaf63a46 < 220b9dfd27f9a21305be2afc75cbe585ddc24e7a`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

### Workarounds

From 1.9.0, bound the number of streams a client can open, for example with http_2_options: [default_local_settings: [max_concurrent_streams: 100]], which bounds the work each frame can cause. From 0.7.0, disabling HTTP/2 with http_2_options: [enabled: false] removes the vulnerable path.