{"id":"CVE-2026-39804","summary":"WebSocket permessage-deflate inflate has no output-size cap in bandit","details":"Allocation 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.","aliases":["EEF-CVE-2026-39804","GHSA-frh3-6pv6-rc8j"],"modified":"2026-05-28T03:55:52.332447001Z","published":"2026-05-01T20:34:24.604Z","database_specific":{"unresolved_ranges":[{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"da4027cff7d2b80319e76fe7a32f84beceec490a"},{"fixed":"8156921a51e684a951221da7bc30a70a022f722e"}]}],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39804.json","cwe_ids":["CWE-770"],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-39804.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-39804"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39804.json"},{"type":"ADVISORY","url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-39804"},{"type":"FIX","url":"https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e"},{"type":"PACKAGE","url":"https://github.com/mtrudel/bandit"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/mtrudel/bandit","events":[{"introduced":"81f0928ec9e92bc70354015435896f03393b1c05"},{"fixed":"e62619895d0d2584d7ffa57d43ef6f72437dfaff"}]}],"versions":["1.10.4","1.10.3","1.10.2","1.10.1","1.10.0","1.9.0","1.8.0","1.7.0","1.6.11","1.6.10","1.6.9","1.6.8","1.6.7","1.6.6","1.6.5","1.6.4","1.6.3","1.6.2","1.6.1","1.6.0","1.5.7","1.5.6","1.5.5","1.5.4","1.5.3","1.5.2","1.5.1","1.5.0","1.4.2","1.4.1","1.4.0","1.3.0","1.2.3","1.2.0","1.1.3","1.1.2","1.1.1","1.1.0","1.0.0","1.0.0-pre.18","1.0.0-pre.17","1.0.0-pre.16","1.0.0-pre.15","1.0.0-pre.14","1.0.0-pre.13","1.0.0-pre.12","1.0.0-pre.11","1.0.0-pre.10","1.0.0-pre.9","1.0.0-pre.8","1.0.0-pre.7","1.0.0-pre.6","1.0.0-pre.5","1.0.0-pre.4","1.0.0-pre.3","1.0.0-pre.2","1.0.0-pre.1","0.7.7","0.7.6","0.7.5","0.7.4","0.7.3","0.7.2","0.7.1","0.7.0","0.6.11","0.6.10","0.6.9","0.6.8","0.6.7","0.6.6","0.6.5","0.6.4","0.6.3","0.6.2","0.6.1","0.6.0","0.5.11","0.5.10","0.5.9"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-39804.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","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"}]}