{"id":"EEF-CVE-2026-111101","summary":"HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit","details":"## Summary\n\nAllocation of Resources Without Limits or Throttling vulnerability in the HTTP/1.1 chunked body reader of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory and CPU via a request body made of many 1-byte chunks.\n\nThe chunked reader in `lib/bandit/http1/socket.ex` keeps every chunk as its own list cell and binary term until `IO.iodata_to_binary/1` joins them, and nothing limits the number of chunks. The `:length` option of `read_body/2` counts only data bytes, so tiny chunks cost far more memory than their payload: 48 MB of 1-byte chunks grew one handler process to about 500 MB and took about 6 s of CPU. The route does not need to read the body, because on keep-alive connections `ensure_completed/1` drains unread bodies through the same reader.\n\nThis issue affects bandit: from 0.1.0 before 1.14.0.\n\n## Details\n\n**1. Per-chunk accumulation.** `do_read_chunked_data!` in `lib/bandit/http1/socket.ex` collects chunks as `[body | chunk]`, adding a cons cell and a binary term for every chunk.\n\n**2. Byte-only limit.** `:length` limits data bytes, not the number of chunks, so a body of `1\\r\\nx\\r\\n` chunks becomes an 8-million-element improper list before `IO.iodata_to_binary` runs. Sending 48 MB of 1-byte chunks grew the handler heap to about 500 MB and used about 6 s of CPU. The same body as one 8 MB chunk peaked at about 16 MB and took 5 ms.\n\n**3. No body read needed.** On keep-alive connections, `ensure_completed/1` drains unread bodies through the same path. Against a Plug that never calls `read_body`, the attack used about 417 MB.\n\n## Proof of concept\n\n1. Run Bandit with a Plug that calls `Plug.Conn.read_body(conn, length: 1_000_000, read_length: 1_000_000)`.\n2. Send `POST /` with `Transfer-Encoding: chunked` and a body of 1,000,000 chunks of `1\\r\\nA\\r\\n`, followed by `0\\r\\n\\r\\n`.\n3. When `read_body` returns the 1,000,000 body bytes, the handler process holds about 48 MB and BEAM memory has grown by about 55 MB, for 6 MB sent.\n\n## Impact\n\nAn unauthenticated client can make a single HTTP/1.1 request hold many times its body size in server memory (about 48 MB for a 1 MB body in the reporter's test), and keep CPU busy while the chunks are joined. This affects any Bandit server that accepts HTTP/1.1 requests, whether or not its routes read the body.\n\n## Workarounds\n\nFrom 0.7.0, a server whose clients and proxies all speak HTTP/2 can disable HTTP/1 with `http_1_options: [enabled: false]`, so that the vulnerable chunked body reader never runs.","aliases":["CVE-2026-111101","GHSA-jwh3-j29h-qfmw"],"modified":"2026-10-26T13:56:06.466616787Z","published":"2026-10-26T13:31:48.184Z","database_specific":{"cwe_ids":["CWE-770"],"capec_ids":["CAPEC-130"],"cpe_ids":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"]},"references":[{"type":"ADVISORY","url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-jwh3-j29h-qfmw"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-111101.html"},{"type":"WEB","url":"https://github.com/mtrudel/bandit/commit/7201270c34b90f6c9e15c0386c2bb802c0c72ab4"},{"type":"FIX","url":"https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a"},{"type":"PACKAGE","url":"https://hex.pm/packages/bandit"}],"affected":[{"package":{"name":"bandit","ecosystem":"Hex","purl":"pkg:hex/bandit"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.1.0"},{"fixed":"1.14.0"}]}],"versions":["0.1.0","0.1.1","0.2.0","0.2.1","0.2.2","0.2.3","0.3.2","0.3.3","0.3.4","0.3.5","0.3.6","0.3.7","0.3.8","0.3.9","0.4.0","0.4.1","0.4.10","0.4.2","0.4.3","0.4.4","0.4.5","0.4.6","0.4.7","0.4.8","0.4.9","0.5.0","0.5.1","0.5.10","0.5.11","0.5.2","0.5.3","0.5.4","0.5.5","0.5.6","0.5.7","0.5.8","0.5.9","0.6.0","0.6.1","0.6.10","0.6.11","0.6.2","0.6.3","0.6.4","0.6.5","0.6.6","0.6.7","0.6.8","0.6.9","0.7.0","0.7.1","0.7.2","0.7.3","0.7.4","0.7.5","0.7.6","0.7.7","1.0.0","1.0.0-pre.1","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-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","1.1.0","1.1.1","1.1.2","1.1.3","1.10.0","1.10.1","1.10.2","1.10.3","1.10.4","1.11.0","1.11.1","1.12.0","1.12.1","1.12.2","1.12.3","1.12.4","1.12.5","1.13.0","1.13.1","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","1.6.10","1.6.11","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.7.0","1.8.0","1.9.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-111101.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/mtrudel/bandit","events":[{"introduced":"7201270c34b90f6c9e15c0386c2bb802c0c72ab4"},{"fixed":"220b9dfd27f9a21305be2afc75cbe585ddc24e7a"}]}],"versions":["1.13.1","1.13.0","1.12.5","1.12.4","1.12.3","1.12.1","1.12.0","1.11.1","1.11.0","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","0.5.8","0.5.7","0.5.6","0.5.5","0.5.4","0.5.3","0.5.2","0.5.1","0.5.0","0.4.10","0.4.9","0.4.8","0.4.7","0.4.6","0.4.5","0.4.4","0.4.3","0.4.2","0.4.1","0.4.0","0.3.9","0.3.8","0.3.7","0.3.6","0.3.5","0.3.4","0.3.3","0.3.2","0.3.1","0.3.0","0.2.3","0.2.2","0.2.1","0.2.0","0.1.1","0.1.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-111101.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Mat Trudel","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}