CVE-2026-108529: Bandit: Quadratic CPU consumption via HTTP/2 SETTINGS frames

Summary

Bandit, an HTTP server for Elixir, is affected by an algorithmic complexity flaw in its HTTP/2 implementation. An unauthenticated remote attacker can open thousands of streams whose responses are blocked by the connection send window, then send small SETTINGS or stream-0 WINDOW_UPDATE frames that each force the server to do quadratic work and keep the CPU busy. The attack requires HTTP/2 to be enabled and affects availability only. A public proof of concept is available.

Affected

Bandit versions before 1.14.0 with HTTP/2 enabled
The start of the affected range is disputed: 0.3.4 according to the CVE record and OSV, 0.3.6 according to the GHSA

Fixed in

Bandit 1.14.0 (fix commit 220b9dfd27f9a21305be2afc75cbe585ddc24e7a)

Workaround

Limit the number of streams per connection, for example with http_2_options: [default_local_settings: [max_concurrent_streams: 100]] (from Bandit 1.9.0)
Disable HTTP/2 with http_2_options: [enabled: false] if HTTP/2 is not required (from 0.7.0). This removes the vulnerable path but is not a code fix.

Exploitation

No exploitation in the wild is known at the time of analysis. No CISA KEV entry was found.
A public proof of concept is available in the GHSA.
CISA SSVC: exploitation none, automatable yes, technical impact partial.

Our recommendation

Upgrade Bandit to 1.14.0 or later, including transitive dependencies in mix.lock, and verify the running version in production.
Until patched, apply the stream limit or disable HTTP/2 where possible.
Check whether internet-facing Phoenix or Bandit services have HTTP/2 enabled.
Monitor CPU usage and response latency of affected services for unusual spikes.

Public exploits

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

CVE Program record (EEF) cna.erlef.org
GitHub Security Advisory GHSA-j363-h72p-296m github.com
Fix commit 220b9df in mtrudel/bandit github.com
OSV record EEF-CVE-2026-108529 osv.dev
Introducing commit 6feadb3 in mtrudel/bandit github.com

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 00:15.

Original description (NVD)

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.

NVD references (5)

Sources

The tracker combines official, freely usable data sources – updated continuously:

NVD (NIST) – CVEs, rating (CVSS), affected products
CISA KEV – vulnerabilities confirmed by CISA as actively exploited
CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
FIRST EPSS – probability of exploitation
Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
PoC-in-GitHub – public proof-of-concept repositories
Metasploit (Rapid7) – modules of the Metasploit Framework
Exploit-DB (OffSec) – archive of public exploits (links only)
Patch days: official vendor pages (linked per vendor) (Vendor patch days)

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