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.

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Solution

No solution given by the vendor.


Workaround

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.

History

Mon, 26 Oct 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 26 Oct 2026 14:00:00 +0000

Type Values Removed Values Added
Description 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.
Title SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked streams in Bandit
First Time appeared Mtrudel
Mtrudel bandit
Weaknesses CWE-407
CPEs cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*
Vendors & Products Mtrudel
Mtrudel bandit
References
Metrics cvssV4_0

{'score': 8.7, 'vector': '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'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-10-26T15:35:50.781Z

Reserved: 2026-10-12T16:15:01.628Z

Link: CVE-2026-108529

cve-icon Vulnrichment

Updated: 2026-10-26T15:32:23.882Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-26T14:16:24.733

Modified: 2026-10-26T16:59:16.113

Link: CVE-2026-108529

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-26T15:45:12Z

Weaknesses