{"id":"CVE-2026-109821","kind":"vulnerability","aliases":["CVE-2026-109821"],"related":[],"title":"Elixir URI module: long port numbers cause CPU exhaustion denial of service","description":"Improper Validation of Specified Quantity in Input vulnerability in the Elixir standard library's URI module allows an attacker who supplies a URL to cause a denial of service through CPU exhaustion.\n\nURI.parse/1 converts the port component with String.to_integer/1 in split_authority/1 (lib/elixir/lib/uri.ex) without bounding its length, so a port of up to 1,262,592 decimal digits produces a bignum of that size and a longer one raises SystemLimitError. Rendering the parsed URI back to text (URI.to_string/1, inspect/1, logging, error formatting) converts the bignum with :erlang.integer_to_binary/1, which is quadratic on Erlang/OTP 27, 28 and 29.0: a 400,000-digit port renders in about 2.6 seconds and a 1 MB port in about 18 seconds. Ports above 65535 are also accepted.\n\nThis issue affects elixir: from 0.5.0 before 1.18.6, from 1.19.0-rc.0 before 1.19.7, and from 1.20.0-rc.0 before 1.20.5.","summary":"Elixir's URI.parse/1 accepts a port with up to about 1.26 million digits and converts it to a huge integer, and rendering that integer back to text is quadratic on Erlang/OTP 27, 28 and 29.0. An attacker who supplies a crafted URL can tie up the CPU for seconds per request, causing denial of service.","severity":"medium","cvss":6.3,"epss":0.00496,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["elixir","erlang-otp","runtime","web-services"],"not_affected_if":["trusted-input-only","unaffected-elixir-version"],"how_to_check":"- Check the Elixir version with `elixir --version`; affected releases are before `1.18.6`, `1.19.0-rc.0` to before `1.19.7`, and `1.20.0-rc.0` to before `1.20.5`.\n- Check the Erlang/OTP version with `erl -noshell -eval 'io:format(\"~s~n\", [erlang:system_info(otp_release)]), halt().'`; OTP 27, 28 and 29.0 are the affected runtimes.\n- Find code paths that call `URI.parse/1` on user-supplied URLs.","fix":"- elixir: move to `1.18.6`, `1.19.7`, or `1.20.5` (or later in the same series).","status":"open","published_at":"2026-10-30T09:17:12+00:00","first_seen_at":"2026-10-30T09:29:38+00:00","triaged_at":"2026-10-30T09:30:41+00:00","updated_at":"2026-10-30T18:23:38+00:00","category":"runtime","confidence":0.8,"triage":{"at":"2026-10-30T09:30:41Z","model":"claude-haiku-5-5","output":{"fix":"- elixir: move to `1.18.6`, `1.19.7`, or `1.20.5` (or later in the same series).","reach":"internet","title":"Elixir URI module: long port numbers cause CPU exhaustion denial of service","impact":"low","summary":"Elixir's URI.parse/1 accepts a port with up to about 1.26 million digits and converts it to a huge integer, and rendering that integer back to text is quadratic on Erlang/OTP 27, 28 and 29.0. An attacker who supplies a crafted URL can tie up the CPU for seconds per request, causing denial of service.","audience":"developers","category":"runtime","nicknames":[],"who_cares":["elixir","erlang-otp","web-services"],"confidence":0.8,"fix_status":"available","needs_auth":"no","worst_case":"Remote requests exhaust CPU and slow or stall the service.","analyst_note":"","how_to_check":"- Check the Elixir version with `elixir --version`; affected releases are before `1.18.6`, `1.19.0-rc.0` to before `1.19.7`, and `1.20.0-rc.0` to before `1.20.5`.\n- Check the Erlang/OTP version with `erl -noshell -eval 'io:format(\"~s~n\", [erlang:system_info(otp_release)]), halt().'`; OTP 27, 28 and 29.0 are the affected runtimes.\n- Find code paths that call `URI.parse/1` on user-supplied URLs.","plain_action":"","needs_analyst":false,"not_affected_if":["trusted-input-only","unaffected-elixir-version"],"who_is_affected":"Any application that parses attacker-supplied URLs with Elixir's URI.parse/1 and then renders or logs the result is exposed. Systems that only handle trusted URLs, or that run an unaffected Elixir release, can skip it.","user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"medium"},"cost_usd":0.000781,"input_tokens":4397,"output_tokens":682,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-109821':15A,18A '-2026':14A,17A '/1':31B,118C '0.5.0':216C '000':188C '1':140C,198C '1.18.6':218C '1.19.0':220C '1.19.7':223C '1.20.0':226C '1.20.5':229C '1.26':39B '18':203C '2.6':194C '262':141C '27':60B,182C '28':61B,183C '29.0':63B,185C '400':187C '592':142C '65535':207C 'accept':32B,210C 'affect':213C 'allow':100C 'also':209C 'attack':65B,102C 'authority/1':128C 'back':53B,161C 'bignum':147C,172C 'binary/1':176C 'bound':131C 'caus':7A,80B,108C 'compon':122C 'convert':43B,119C,170C 'cpu':8A,75B,114C 'craft':69B 'cve':13A,16A 'decim':143C 'denial':10A,81B,110C 'digit':41B,144C,189C 'elixir':1A,19B,27B,94C,214C 'erlang':21B 'erlang-otp':20B 'erlang.integer':174C 'erlang/otp':59B,181C 'error':168C 'exhaust':9A,115C 'format':169C 'huge':47B 'improp':84C 'input':90C 'inspect/1':166C 'integ':48B,52B 'integer/1':125C 'issu':212C 'length':133C 'lib/elixir/lib/uri.ex':129C 'librari':96C 'log':167C 'long':4A 'longer':153C 'mb':199C 'million':40B 'modul':3A,99C 'number':6A 'one':154C 'otp':22B 'pars':159C 'per':78B 'port':5A,34B,121C,136C,190C,200C,205C 'produc':145C 'quadrat':57B,179C 'quantiti':88C 'rais':155C 'rc.0':221C,227C 'render':50B,157C,191C 'request':79B 'runtim':23B 'second':77B,195C,204C 'servic':12A,26B,83B,112C 'size':150C 'specifi':87C 'split':127C 'standard':95C 'string.to':124C 'string/1':165C 'suppli':67B,104C 'systemlimiterror':156C 'text':55B,163C 'tie':72B 'uri':2A,98C,160C 'uri.parse':30B,117C 'uri.parse/1':29B,116C 'uri.to':164C 'url':70B,106C 'valid':85C 'vulner':91C 'web':25B 'web-servic':24B 'without':130C","nicknames":[],"mitigations":[],"who_affected":"Any application that parses attacker-supplied URLs with Elixir's URI.parse/1 and then renders or logs the result is exposed. Systems that only handle trusted URLs, or that run an unaffected Elixir release, can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"first_public_at":"2026-10-30T09:17:12+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/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","cvss_by":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-109821","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-109821","severity":null,"published_at":"2026-10-30T09:17:12+00:00","modified_at":"2026-10-30T09:17:12+00:00","first_seen_at":"2026-10-30T09:29:38+00:00","fetched_at":"2026-10-30T09:29:38+00:00","note":null},{"source":"epss","external_id":"CVE-2026-109821","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-109821","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-30T18:23:38+00:00","fetched_at":"2026-10-30T18:23:38+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}