{"affected":[{"package":{"ecosystem":"Hex","name":"bandit","purl":"pkg:hex/bandit"},"ranges":[{"events":[{"introduced":"0.5.9"},{"fixed":"1.11.0"}],"type":"SEMVER"}],"versions":["0.5.9","0.5.10","0.5.11","0.6.0","0.6.1","0.6.2","0.6.3","0.6.4","0.6.5","0.6.6","0.6.7","0.6.8","0.6.9","0.6.10","0.6.11","0.7.0","0.7.1","0.7.2","0.7.3","0.7.4","0.7.5","0.7.6","0.7.7","1.0.0-pre.1","1.0.0-pre.2","1.0.0-pre.3","1.0.0-pre.4","1.0.0-pre.5","1.0.0-pre.6","1.0.0-pre.7","1.0.0-pre.8","1.0.0-pre.9","1.0.0-pre.10","1.0.0-pre.11","1.0.0-pre.12","1.0.0-pre.13","1.0.0-pre.14","1.0.0-pre.15","1.0.0-pre.16","1.0.0-pre.17","1.0.0-pre.18","1.0.0","1.1.0","1.1.1","1.1.2","1.1.3","1.2.0","1.2.1","1.2.2","1.2.3","1.3.0","1.4.0","1.4.1","1.4.2","1.5.0","1.5.1","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.6.10","1.6.11","1.7.0","1.8.0","1.9.0","1.10.0","1.10.1","1.10.2","1.10.3","1.10.4"]},{"ranges":[{"events":[{"introduced":"da4027cff7d2b80319e76fe7a32f84beceec490a"},{"fixed":"1.11.0"}],"repo":"https://github.com/mtrudel/bandit","type":"GIT"}]}],"aliases":["GHSA-frh3-6pv6-rc8j","CVE-2026-39804"],"credits":[{"name":"Peter Ullrich","type":"FINDER"}],"database_specific":{"capec_ids":["CAPEC-130"],"cpe_ids":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-770"]},"details":"## Summary\n\nAllocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.\n\n'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.\n\nAn unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill.\n\nThis vulnerability requires both Bandit's server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false.\n\nThis issue affects bandit: from 0.5.9 before 1.11.0.\n\n## Workaround\n\nDo not pass compress: true to WebSockAdapter.upgrade/4. Omitting this option (or setting it to false) prevents permessage-deflate from being negotiated, so the inflate path is never reached.\n\n## Configuration\n\nThe vulnerability is only reachable when both of the following conditions are true:\n- Bandit's server-level websocket_options.compress is enabled (it defaults to true).\n- The per-upgrade compress: true option is passed to WebSockAdapter.upgrade/4 (it defaults to false; Phoenix's default is also false).\n\nStock Phoenix and LiveView applications are not affected because compress: false is their default.","id":"EEF-CVE-2026-39804","modified":"2026-05-01T20:34:24.604Z","published":"2026-05-01T20:34:24.604Z","references":[{"type":"ADVISORY","url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-39804.html"},{"type":"FIX","url":"https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e"},{"type":"PACKAGE","url":"https://hex.pm/packages/bandit"}],"related":[],"schema_version":"1.7.3","severity":[{"score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","type":"CVSS_V4"}],"summary":"WebSocket permessage-deflate inflate has no output-size cap in bandit","upstream":[]}