{"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","slug":"CVE-2026-108529","body":"## Overview\n\nInefficient 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.\n\ndo_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.\n\nThis issue affects bandit: from 0.3.4 before 1.14.0.\n\n## Affected\n\n- `bandit >= 0.3.4 < 1.14.0`\n- `mtrudel/bandit >= 6feadb31189d18b7dcda6c663112cd3bbaf63a46 < 220b9dfd27f9a21305be2afc75cbe585ddc24e7a`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n### Workarounds\n\nFrom 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.","depth":"twilight","depthScore":48,"depthScoreParts":{"impact":47.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}