{"id":"CVE-2026-129122","kind":"vulnerability","aliases":["CVE-2026-129122"],"related":[],"title":"C-Kermit: Telnet server can overflow client memory via environment variables","description":"C-Kermit 6.0.192 before 11.1.515 contains a buffer overflow vulnerability in tn_snenv() in ckctel.c that allows malicious Telnet servers to corrupt client memory via crafted NEW-ENVIRON SEND subnegotiation. Malicious or machine-in-the-middle servers can send oversized variable names before authentication, overflowing a 16-byte stack buffer and a miscomputed heap buffer to corrupt stack and heap memory.","summary":"C-Kermit 6.0.192 through versions before 11.1.515 has a buffer overflow in its Telnet NEW-ENVIRON handling. A malicious or man-in-the-middle Telnet server can send oversized variable names before authentication, corrupting stack and heap memory in the client.","severity":"high","cvss":7.7,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["c-kermit","linux","package","telnet","unix"],"not_affected_if":["no-telnet-use","trusted-servers-only"],"how_to_check":"- Run `kermit` and check the version banner for a release earlier than `11.1.515`\n- Check whether the Telnet client is used to connect to servers you do not fully control","fix":"- C-Kermit: move to `11.1.515` or later (the fixed version named in the product range)","status":"open","published_at":"2026-11-13T17:17:29+00:00","first_seen_at":"2026-11-13T17:48:00+00:00","triaged_at":"2026-11-13T17:48:48+00:00","updated_at":"2026-11-13T17:48:48+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-11-13T17:48:48Z","model":"claude-haiku-5-5","output":{"fix":"- C-Kermit: move to `11.1.515` or later (the fixed version named in the product range)","reach":"network","title":"C-Kermit: Telnet server can overflow client memory via environment variables","impact":"high","summary":"C-Kermit 6.0.192 through versions before 11.1.515 has a buffer overflow in its Telnet NEW-ENVIRON handling. A malicious or man-in-the-middle Telnet server can send oversized variable names before authentication, corrupting stack and heap memory in the client.","audience":"developers","category":"package","nicknames":[],"who_cares":["c-kermit","telnet","linux","unix"],"confidence":0.7,"fix_status":"available","needs_auth":"no","worst_case":"malicious server corrupts client memory, possibly running attacker code","analyst_note":"Confirm the Telnet NEW-ENVIRON trigger conditions and whether the exploit path needs the Telnet option enabled, using the vendor advisory and vulncheck page.","how_to_check":"- Run `kermit` and check the version banner for a release earlier than `11.1.515`\n- Check whether the Telnet client is used to connect to servers you do not fully control","plain_action":"","product_name":"","needs_analyst":true,"not_affected_if":["no-telnet-use","trusted-servers-only"],"who_is_affected":"Any team running C-Kermit's Telnet client to connect to remote hosts, especially to servers outside their control or across untrusted networks. The flaw is triggered by the server side, so a client that only talks to trusted Telnet hosts has much lower exposure. unknown whether the sources describe any other usage path.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000778,"input_tokens":4711,"output_tokens":613,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-129122':15A,18A '-2026':14A,17A '11.1.515':33B,75C '16':119C '6.0.192':29B,73C 'allow':87C 'authent':61B,116C 'buffer':36B,78C,122C,127C 'byte':120C 'c':2A,20B,27B,71C 'c-kermit':1A,19B,26B,70C 'ckctel.c':85C 'client':8A,69B,93C 'contain':76C 'corrupt':62B,92C,129C 'craft':96C 'cve':13A,16A 'environ':11A,43B,99C 'handl':44B 'heap':65B,126C,132C 'kermit':3A,21B,28B,72C 'linux':22B 'machin':105C 'machine-in-the-middl':104C 'malici':46B,88C,102C 'man':49B 'man-in-the-middl':48B 'memori':9A,66B,94C,133C 'middl':52B,108C 'miscomput':125C 'name':59B,114C 'new':42B,98C 'new-environ':41B,97C 'overflow':7A,37B,79C,117C 'overs':57B,112C 'packag':23B 'send':56B,100C,111C 'server':5A,54B,90C,109C 'snenv':83C 'stack':63B,121C,130C 'subnegoti':101C 'telnet':4A,24B,40B,53B,89C 'tn':82C 'unix':25B 'variabl':12A,58B,113C 'version':31B 'via':10A,95C 'vulner':80C","nicknames":[],"mitigations":[],"who_affected":"Any team running C-Kermit's Telnet client to connect to remote hosts, especially to servers outside their control or across untrusted networks. The flaw is triggered by the server side, so a client that only talks to trusted Telnet hosts has much lower exposure. unknown whether the sources describe any other usage path.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["ckermit","high","linux","package","telnet","unix"],"campaign_type":null,"search_a":"'-129122':15A,18A '-2026':14A,17A 'c':2A 'c-kermit':1A 'client':8A 'cve':13A,16A 'environ':11A 'kermit':3A 'memori':9A 'overflow':7A 'server':5A 'telnet':4A 'variabl':12A 'via':10A","search_b":"'11.1.515':33B '6.0.192':29B 'authent':61B 'buffer':36B 'c':20B,27B 'c-kermit':19B,26B 'client':69B 'corrupt':62B 'environ':43B 'handl':44B 'heap':65B 'kermit':21B,28B 'linux':22B 'malici':46B 'man':49B 'man-in-the-middl':48B 'memori':66B 'middl':52B 'name':59B 'new':42B 'new-environ':41B 'overflow':37B 'overs':57B 'packag':23B 'send':56B 'server':54B 'stack':63B 'telnet':24B,40B,53B 'unix':25B 'variabl':58B 'version':31B","search_c":"'11.1.515':75C '16':119C '6.0.192':73C 'allow':87C 'authent':116C 'buffer':78C,122C,127C 'byte':120C 'c':71C 'c-kermit':70C 'ckctel.c':85C 'client':93C 'contain':76C 'corrupt':92C,129C 'craft':96C 'environ':99C 'heap':126C,132C 'kermit':72C 'machin':105C 'machine-in-the-middl':104C 'malici':88C,102C 'memori':94C,133C 'middl':108C 'miscomput':125C 'name':114C 'new':98C 'new-environ':97C 'overflow':79C,117C 'overs':112C 'send':100C,111C 'server':90C,109C 'snenv':83C 'stack':121C,130C 'subnegoti':101C 'telnet':89C 'tn':82C 'variabl':113C 'via':95C 'vulner':80C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-10-31T01:36:44+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/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","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-129122","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-129122","severity":null,"published_at":"2026-11-13T17:17:29+00:00","modified_at":"2026-11-13T17:17:29+00:00","first_seen_at":"2026-11-13T17:48:00+00:00","fetched_at":"2026-11-13T17:48:00+00:00","note":null}],"documents":[{"id":148099,"url":"https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":148100,"url":"https://github.com/OpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955d25","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":148076,"url":"https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515","title":"Release notes: github.com","kind":"release","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Release notes: github.com"},{"id":148102,"url":"https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-31T01:36:44+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":148103,"url":"https://www.vulncheck.com/advisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via-telnet-new-environ-negotiation","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"}],"disclosures":[],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}