{"id":"CVE-2026-42786","aliases":["EEF-CVE-2026-42786","GHSA-pf94-94m9-536p"],"url":"https://o3.security/vulnerability/CVE-2026-42786","summary":"WebSocket fragmented message reassembly unbounded in bandit","details":"Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion.\n\nThe fragment reassembly path in 'Elixir.Bandit.WebSocket.Connection':handle_frame/3 in lib/bandit/websocket/connection.ex appends every incoming Continuation{fin: false} frame's payload to a per-connection iolist with no cumulative size cap. The existing max_frame_size option only bounds individual frames; a peer that streams an unbounded number of continuation frames without ever setting fin=1 grows BEAM heap linearly until the OS or a supervisor kills the process.\n\nBecause the accumulation happens before WebSock.handle_in/2 is called, the application has no opportunity to interpose a size check. Phoenix Channels and LiveView both run over WebSock on Bandit, so a stock Phoenix application exposes this surface as soon as it accepts socket connections.\n\nThis issue affects bandit: from 0.5.0 before 1.11.0.","published":"2026-05-01T20:34:17.014Z","modified":"2026-08-07T11:50:18.748234514Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Hex","name":"bandit","fixedVersion":"1.11.0"}],"fix":{"url":"https://github.com/mtrudel/bandit/commit/21612c7c7b1ce43eccd36d3af3a2299d23513667","label":"mtrudel/bandit@21612c7"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-42786.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-42786"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42786.json"},{"type":"ADVISORY","url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-pf94-94m9-536p"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42786"},{"type":"FIX","url":"https://github.com/mtrudel/bandit/commit/21612c7c7b1ce43eccd36d3af3a2299d23513667"},{"type":"PACKAGE","url":"https://github.com/mtrudel/bandit"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:50:18.748234514Z"}}