{"id":"CVE-2026-83813","kind":"vulnerability","aliases":["CVE-2026-83813"],"related":[],"title":"Twisted: DNS resolver accepts forged UDP answers from any source","description":"Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.names.dns.DNSDatagramProtocol accepts a UDP DNS response for a pending query when its 16-bit transaction ID matches but does not verify that the response came from the queried host and port. An attacker able to deliver a packet to the resolver's listening port with the correct transaction ID can inject a forged answer. The standard twisted.names.client.Resolver uses a new random source port for each query, increasing off-path attack complexity, while applications that reuse a DNSDatagramProtocol instance expose only the transaction-ID search space after the first query. A successful forgery can redirect hostname resolution and enable mail interception, server-side request forgery, or man-in-the-middle positioning. This issue is fixed in version 26.10.0rc1.","summary":"Twisted's DNS datagram protocol accepts a UDP reply whose 16-bit transaction ID matches a pending query without checking the sender's address and port. An off-path attacker who can send packets to the resolver and guess the transaction ID can inject a fake answer, redirecting hostname lookups for mail interception, SSRF or man-in-the-middle positioning.","severity":"low","cvss":3.1,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["package","python","self-hosted","twisted"],"not_affected_if":["no-twisted-dns-use"],"how_to_check":"- Check the installed Twisted version with `python -c \"import twisted; print(twisted.__version__)\"` or `pip show twisted`\n- Look for code that reuses a single `DNSDatagramProtocol` instance for multiple queries, since the search space is reduced after the first query","fix":"- Upgrade Twisted to `26.10.0rc1` or later","status":"open","published_at":"2026-10-23T21:17:25+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","triaged_at":"2026-10-25T04:47:16+00:00","updated_at":"2026-10-25T04:47:16+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-25T04:47:16Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade Twisted to `26.10.0rc1` or later","reach":"internet","title":"Twisted: DNS resolver accepts forged UDP answers from any source","impact":"medium","summary":"Twisted's DNS datagram protocol accepts a UDP reply whose 16-bit transaction ID matches a pending query without checking the sender's address and port. An off-path attacker who can send packets to the resolver and guess the transaction ID can inject a fake answer, redirecting hostname lookups for mail interception, SSRF or man-in-the-middle positioning.","category":"package","nicknames":[],"who_cares":["python","twisted","self-hosted"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker forges DNS answers, redirecting hostname resolution and traffic","analyst_note":"","how_to_check":"- Check the installed Twisted version with `python -c \"import twisted; print(twisted.__version__)\"` or `pip show twisted`\n- Look for code that reuses a single `DNSDatagramProtocol` instance for multiple queries, since the search space is reduced after the first query","needs_analyst":false,"not_affected_if":["no-twisted-dns-use"],"who_is_affected":"Applications that perform DNS resolution through Twisted's twisted.names DNS code, especially those that reuse one DNSDatagramProtocol instance, are exposed. Standard twisted.names.client.Resolver use with per-query random source ports is harder to attack, but the sources still call it affected before the fix. Applications that do not use twisted.names for DNS lookups can skip it.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"low"},"cost_usd":0.000644,"input_tokens":3494,"output_tokens":589,"severity_before":"low"},"analyst_status":null,"analyst_note":null,"search":"'-2026':12A,15A '-83813':13A,16A '16':33B,114C '26.10.0':100C,222C '3.6':97C 'abl':135C 'accept':4A,28B,103C 'address':46B 'answer':7A,70B,155C 'applic':94C,175C 'attack':53B,134C,172C 'base':90C 'bit':34B,115C 'came':126C 'check':42B 'complex':173C 'correct':148C 'cve':11A,14A 'datagram':26B 'deliv':137C 'dns':2A,25B,106C 'dnsdatagramprotocol':179C 'enabl':201C 'event':89C 'event-bas':88C 'expos':181C 'fake':69B 'first':191C 'fix':219C 'forg':5A,154C 'forgeri':195C,208C 'framework':91C 'guess':62B 'host':21B,130C 'hostnam':72B,198C 'id':36B,65B,117C,150C,186C 'increas':168C 'inject':67B,152C 'instanc':180C 'intercept':76B,203C 'internet':93C 'issu':217C 'listen':144C 'lookup':73B 'mail':75B,202C 'man':80B,211C 'man-in-the-middl':79B,210C 'match':37B,118C 'middl':83B,214C 'new':161C 'off-path':50B,169C 'packag':17B 'packet':57B,139C 'path':52B,171C 'pend':39B,110C 'port':48B,132C,145C,164C 'posit':84B,215C 'prior':98C 'protocol':27B 'python':18B,96C 'queri':40B,111C,129C,167C,192C 'random':162C 'rc1':101C,223C 'redirect':71B,197C 'repli':31B 'request':207C 'resolut':199C 'resolv':3A,60B,142C 'respons':107C,125C 'reus':177C 'search':187C 'self':20B 'self-host':19B 'send':56B 'sender':44B 'server':205C 'server-sid':204C 'side':206C 'sourc':10A,163C 'space':188C 'ssrf':77B 'standard':157C 'success':194C 'support':95C 'transact':35B,64B,116C,149C,185C 'transaction-id':184C 'twist':1A,22B,23B,85C 'twisted.names.client.resolver':158C 'twisted.names.dns.dnsdatagramprotocol':102C 'udp':6A,30B,105C 'use':159C 'verifi':122C 'version':221C 'whose':32B 'without':41B","nicknames":[],"mitigations":[],"who_affected":"Applications that perform DNS resolution through Twisted's twisted.names DNS code, especially those that reuse one DNSDatagramProtocol instance, are exposed. Standard twisted.names.client.Resolver use with per-query random source ports is harder to attack, but the sources still call it affected before the fix. Applications that do not use twisted.names for DNS lookups can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T21:17:25+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","cvss_by":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-83813","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-83813","severity":null,"published_at":"2026-10-23T21:17:25+00:00","modified_at":"2026-10-23T21:17:25+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T22:29:04+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"}