{"id":"CVE-2026-123612","kind":"vulnerability","aliases":["CVE-2026-123612"],"related":[],"title":"rustls: early application data sent to wrong server when ECH rejected","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","summary":"rustls 0.23.44 and 0.23.45 send application data queued before the handshake completes to the public_name server when Encrypted Client Hello is rejected. The authenticated public-facing server, not the intended inner server, receives data meant for the inner server, which can leak it.","severity":"medium","cvss":4.6,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ech","package","rust","rustls","tls"],"not_affected_if":["no-ech","other-rustls-version"],"how_to_check":"- Check the rustls version in `Cargo.lock` for `rustls` `0.23.44` or `0.23.45`\n- Check whether the application enables Encrypted Client Hello on its client connections","fix":"- Move `rustls` past `0.23.45` (the sources do not name the fixed version)","status":"open","published_at":"2026-11-08T02:16:56+00:00","first_seen_at":"2026-11-08T02:21:14+00:00","triaged_at":"2026-11-08T02:25:35+00:00","updated_at":"2026-11-08T02:25:35+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-11-08T02:25:35Z","model":"claude-haiku-5-5","output":{"fix":"- Move `rustls` past `0.23.45` (the sources do not name the fixed version)","reach":"network","title":"rustls: early application data sent to wrong server when ECH rejected","impact":"medium","summary":"rustls 0.23.44 and 0.23.45 send application data queued before the handshake completes to the public_name server when Encrypted Client Hello is rejected. The authenticated public-facing server, not the intended inner server, receives data meant for the inner server, which can leak it.","audience":"developers","category":"package","nicknames":[],"who_cares":["rust","rustls","tls","ech"],"confidence":0.6,"fix_status":"unknown","needs_auth":"no","worst_case":"data meant for inner server leaks to public server","analyst_note":"Confirm the fixed rustls version and the advisory details at the linked vendor advisory on github.com and the vulncheck.com page.","how_to_check":"- Check the rustls version in `Cargo.lock` for `rustls` `0.23.44` or `0.23.45`\n- Check whether the application enables Encrypted Client Hello on its client connections","plain_action":"","needs_analyst":true,"not_affected_if":["no-ech","other-rustls-version"],"who_is_affected":"Applications using rustls 0.23.44 or 0.23.45 as a TLS client with Encrypted Client Hello configured can send early plaintext to the public_name server when ECH is rejected. Clients that do not use ECH, and servers using rustls, are not described as affected by the sources.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.000708,"input_tokens":4292,"output_tokens":558,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-123612':14A,17A '-2026':13A,16A '0.23.44':24B,68C '0.23.45':26B,70C 'alert':110C 'applic':3A,28B,78C 'authent':47B,112C 'buffer':80C 'client':42B,88C,93C 'client-fac':87C 'clientconnect':103C 'complet':34B,84C 'contain':71C 'cve':12A,15A 'data':4A,29B,58B,79C,117C 'disclosur':74C 'earli':2A 'ech':10A,18B,108C 'encrypt':41B,92C 'face':50B,89C 'handshak':33B,83C 'hello':43B,94C 'inform':73C 'inner':55B,62B,121C 'intend':54B,118C 'leak':66B 'meant':59B 'name':38B,114C 'packag':19B 'plaintext':101C 'public':37B,49B,113C 'public-fac':48B 'queu':30B 'queue':100C 'receiv':57B,116C 'reject':11A,45B,96C 'requir':109C 'rust':20B 'rustl':1A,21B,23B,67C 'send':27B,77C,106C 'sent':5A 'server':8A,39B,51B,56B,63B,90C,115C,122C 'start':98C 'tls':22B 'traffic':99C 'vulner':75C 'writer':104C 'wrong':7A","nicknames":[],"mitigations":[],"who_affected":"Applications using rustls 0.23.44 or 0.23.45 as a TLS client with Encrypted Client Hello configured can send early plaintext to the public_name server when ECH is rejected. Clients that do not use ECH, and servers using rustls, are not described as affected by the sources.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"unknown","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["ech","medium","package","rust","rustls","tls"],"campaign_type":null,"search_a":"'-123612':14A,17A '-2026':13A,16A 'applic':3A 'cve':12A,15A 'data':4A 'earli':2A 'ech':10A 'reject':11A 'rustl':1A 'sent':5A 'server':8A 'wrong':7A","search_b":"'0.23.44':24B '0.23.45':26B 'applic':28B 'authent':47B 'client':42B 'complet':34B 'data':29B,58B 'ech':18B 'encrypt':41B 'face':50B 'handshak':33B 'hello':43B 'inner':55B,62B 'intend':54B 'leak':66B 'meant':59B 'name':38B 'packag':19B 'public':37B,49B 'public-fac':48B 'queu':30B 'receiv':57B 'reject':45B 'rust':20B 'rustl':21B,23B 'send':27B 'server':39B,51B,56B,63B 'tls':22B","search_c":"'0.23.44':68C '0.23.45':70C 'alert':110C 'applic':78C 'authent':112C 'buffer':80C 'client':88C,93C 'client-fac':87C 'clientconnect':103C 'complet':84C 'contain':71C 'data':79C,117C 'disclosur':74C 'ech':108C 'encrypt':92C 'face':89C 'handshak':83C 'hello':94C 'inform':73C 'inner':121C 'intend':118C 'name':114C 'plaintext':101C 'public':113C 'queue':100C 'receiv':116C 'reject':96C 'requir':109C 'rustl':67C 'send':77C,106C 'server':90C,115C,122C 'start':98C 'traffic':99C 'vulner':75C 'writer':104C","first_public_at":"2026-10-14T09:55:10+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/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":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-123612","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-123612","severity":null,"published_at":"2026-11-08T02:16:56+00:00","modified_at":"2026-11-08T02:16:56+00:00","first_seen_at":"2026-11-08T02:21:14+00:00","fetched_at":"2026-11-08T02:21:14+00:00","note":null}],"documents":[{"id":99375,"url":"https://github.com/rustls/rustls/security/advisories/GHSA-vp88-798v-h67f","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-14T09:55:10+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":99376,"url":"https://www.vulncheck.com/advisories/rustls-0.23.44-and-0.23.45-ech-rejection-application-data-disclosure","title":"Third-party advisory: www.vulncheck.com","kind":"advisory","source":"nvd","publisher":"research","text":null,"published_at":null,"relation":"advisory","confidence":null,"note":"Third-party advisory: www.vulncheck.com"}],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}