{"id":"CVE-2026-113436","aliases":["EEF-CVE-2026-113436","EUVD-2026-109823","GHSA-29cr-8477-rg6r","UBUNTU-CVE-2026-113436"],"status":"published","title":"Quadratic bignum parsing of Content-Length and Host port values in Bandit","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.\n\nBandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","severity":{"version":"4.0","score":8.7,"vector":"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00602,"percentile":0.49331,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-407"],"published":"2026-10-26T13:31:35Z","modified":"2026-11-11T02:48:41Z","fixes":[{"ecosystem":"Hex","package":"bandit","fixed_in":["1.14.0"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Hex","package":"bandit","ranges":[{"type":"SEMVER","events":[{"introduced":"1.0.0-pre.7"},{"fixed":"1.14.0"}]}],"versions":["1.0.0","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.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"]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.13.2-1","0.13.2-3"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.0-0ubuntu2"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.1-3","1.6.2-1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.6.2-1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.6.2-3"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.7.10-3","1.9.4-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"bandit","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.7.10-2","1.7.10-3"]}],"products":[{"vendor":"mtrudel","product":"bandit"}],"references":[{"url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-29cr-8477-rg6r","tags":["vendor-advisory","related","advisory"]},{"url":"https://cna.erlef.org/cves/CVE-2026-113436.html","tags":["related","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-113436","tags":["related","web"]},{"url":"https://github.com/mtrudel/bandit/commit/e0c8c0c30af9b0f57d8aafac37ddd9294363a8be","tags":["related","fix","web","report"]},{"url":"https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a","tags":["patch","fix","report"]},{"url":"https://github.com","tags":["web","report"]},{"url":"https://repo.hex.pm","tags":["web","report"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/113xxx/CVE-2026-113436.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-113436","tags":["advisory"]},{"url":"https://github.com/mtrudel/bandit","tags":["package","report"]},{"url":"https://hex.pm/packages/bandit","tags":["package","report"]},{"url":"https://ubuntu.com/security/CVE-2026-113436","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-113436","tags":["report"]},{"url":"https://cna.erlef.org/cves/cve-2026-113436.html","tags":["report"]},{"url":"https://github.com/mtrudel/bandit/security/advisories/ghsa-29cr-8477-rg6r","tags":["report"]},{"url":"https://github.com/cveproject/cvelistv5/tree/main/cves/2026/113xxx/cve-2026-113436.json","tags":["report"]},{"url":"https://nvd.nist.gov/vuln/detail/cve-2026-113436","tags":["report"]},{"url":"https://osv.dev/vulnerability/eef-cve-2026-113436","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-113436","title":"Quadratic bignum parsing of Content-Length and Host port values in Bandit","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.\n\nBandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","status":"published","published":"2026-10-26T13:31:35.033Z","modified":"2026-10-26T15:35:51.556Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high","assessor":"cna"}],"cwes":["CWE-407"],"updated_at":"2026-11-02T13:44:29.519518Z"}],"euvd":[{"id":"EUVD-2026-109823","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.\n\nBandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","status":"published","published":"2026-10-26T13:31:35Z","modified":"2026-10-26T15:35:51Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"updated_at":"2026-11-02T16:59:29.561971Z"}],"nvd":[{"id":"CVE-2026-113436","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.\n\nBandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","status":"published","published":"2026-10-26T14:16:28.68Z","modified":"2026-10-26T16:59:16.113Z","cvss":[{"version":"4.0","score":8.7,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"high","assessor":"secondary"}],"cwes":["CWE-407"],"updated_at":"2026-11-02T14:13:03.452847Z"}],"osv":[{"id":"CVE-2026-113436","title":"Quadratic bignum parsing of Content-Length and Host port values in Bandit","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.\n\nBandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","status":"published","published":"2026-10-26T13:31:35.033Z","modified":"2026-11-11T10:47:23.335398101Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-407"],"updated_at":"2026-11-11T03:22:04.464623Z"},{"id":"EEF-CVE-2026-113436","title":"Quadratic bignum parsing of Content-Length and Host port values in Bandit","description":"## Summary\n\nInefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a `content-length` value or a `Host` or `:authority` port made of thousands of digits.\n\n`Bandit.Headers.parse_integer/2` in `lib/bandit/headers.ex` builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.\n\nThis issue affects bandit: from 1.0.0-pre.7 before 1.14.0.\n\n## Details\n\n**1. Unbounded digit loop.** `Bandit.Headers.parse_integer/2` in `lib/bandit/headers.ex` builds the number with `total * 10 + digit - ?0` and has no limit on the digit count. Each step allocates a new bignum, so parsing one value costs O(n²). On OTP 28, 10,000 digits take about 10 ms, 50,000 about 250 ms and 80,000 about 560 ms, where `String.to_integer/1` handles the same inputs in 1 to 3 ms.\n\n**2. Reached on raw input.** It is called from `get_content_length/1` and `parse_hostlike_header!/1` on raw request input, before any range check. An all-digit `content-length` is returned as `{:ok, huge_int}`, and the `is_port_number` guard only runs after the whole number is built.\n\n**3. HPACK amplification.** Over HTTP/2, a 4,000-digit value (about 1.1 ms to parse) can be stored once in the HPACK dynamic table and then re-sent on each new stream for about one byte.\n\n## Proof of concept\n\n1. Run Bandit with any Plug.\n2. Open an HTTP/2 connection with prior knowledge and complete the SETTINGS exchange.\n3. In one write, send 5,000 HEADERS frames for `POST /` on new streams, each carrying a `content-length` of 4,000 `9` digits encoded with HPACK indexing, so that every frame after the first refers to the stored value.\n4. The 124,003 bytes take 27.9 s to process before all 5,000 requests reach the Plug.\n\n## Impact\n\nAn unauthenticated client can make the server spend CPU time out of all proportion to the traffic it sends (27.9 s for 124 KB in the reporter's test). This affects any Bandit server reachable by untrusted clients over HTTP/1 or HTTP/2, with no special configuration.","status":"published","published":"2026-10-26T13:31:35.033Z","modified":"2026-10-26T13:56:06.731234193Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-407"],"updated_at":"2026-11-02T15:46:33.047032Z"},{"id":"UBUNTU-CVE-2026-113436","description":"Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits. Bandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s. This issue affects bandit: from 1.0.0-pre.7 before 1.14.0.","status":"published","published":"2026-10-26T14:16:00Z","modified":"2026-10-28T20:15:44.975590222Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"},{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"updated_at":"2026-11-02T16:55:59.591851Z"}]}}