What’s Vulnerable › Vulnerabilities

CVE-2026-108529: SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked streams in Bandit

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-26 · updated 2026-10-26
• Weakness: CWE-407

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.

Affected products

• mtrudel bandit: from 0.3.4 before 1.14.0 — fixed in 1.14.0

How to fix

Upgrade to a fixed version: mtrudel bandit 1.14.0. Check the vendor advisory for mitigations.

References

• https://cna.erlef.org/cves/CVE-2026-108529.html
• https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a
• https://github.com/mtrudel/bandit/commit/6feadb31189d18b7dcda6c663112cd3bbaf63a46
• https://github.com/mtrudel/bandit/security/advisories/GHSA-j363-h72p-296m
• https://osv.dev/vulnerability/EEF-CVE-2026-108529

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