{"id":"CVE-2026-20197","kind":"vulnerability","aliases":["CVE-2026-20197"],"related":[],"title":"Cisco Snort 3: crafted Teredo packet crashes packet inspection engine","description":"Multiple Cisco products are affected by a vulnerability in the Snort 3 Teredo Detection Engine that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart, resulting in an interruption of packet inspection.\r\n\r\nThis vulnerability is due to incomplete error checking when Snort 3 parses Teredo packets. An attacker could exploit this vulnerability by sending a crafted Teredo packet to a targeted device to be parsed by Snort. A successful exploit could allow the attacker to cause the Snort 3 Detection Engine to restart unexpectedly, resulting in a DoS condition.","summary":"Snort 3, the intrusion detection engine shipped in several Cisco products, mishandles certain Teredo tunnel packets because error checking is incomplete. A remote attacker without credentials can send one crafted packet to make the Snort 3 detection engine restart, interrupting packet inspection.","severity":"medium","cvss":5.8,"epss":0.0039,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["cisco","ids-ips","infrastructure","network-security","snort-3"],"not_affected_if":["no-teredo-inspection","snort-2"],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-21T17:18:27+00:00","first_seen_at":"2026-10-23T21:57:29+00:00","triaged_at":"2026-10-25T04:10:03+00:00","updated_at":"2026-10-25T04:10:03+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-25T04:10:03Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"network","title":"Cisco Snort 3: crafted Teredo packet crashes packet inspection engine","impact":"low","summary":"Snort 3, the intrusion detection engine shipped in several Cisco products, mishandles certain Teredo tunnel packets because error checking is incomplete. A remote attacker without credentials can send one crafted packet to make the Snort 3 detection engine restart, interrupting packet inspection.","category":"infrastructure","nicknames":[],"who_cares":["cisco","snort-3","network-security","ids-ips"],"confidence":0.6,"needs_auth":"no","worst_case":"Packet inspection stops until the Snort 3 engine restarts again","analyst_note":"Check the Cisco advisory for the affected product list, fixed software versions and whether Teredo inspection is on by default; the NVD entry in the sources does not give them.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["snort-2","no-teredo-inspection"],"who_is_affected":"Organizations running Cisco products that include the Snort 3 detection engine with Teredo detection active, where inspection traffic reaches the device from untrusted networks. Teams not running Cisco products with Snort 3 can skip it.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000585,"input_tokens":3478,"output_tokens":474,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-20197':13A,16A '-2026':12A,15A '-3':26B '3':3A,28B,62B,80C,95C,117C,153C 'affect':73C 'allow':86C,146C 'attack':50B,90C,122C,148C 'caus':92C,150C 'certain':39B 'check':45B,114C 'cisco':1A,17B,36B,70C 'condit':163C 'could':85C,123C,145C 'craft':4A,56B,130C 'crash':7A 'credenti':52B 'cve':11A,14A 'detect':31B,63B,82C,96C,154C 'devic':136C 'dos':162C 'due':110C 'engin':10A,32B,64B,83C,97C,155C 'error':44B,113C 'exploit':124C,144C 'id':19B 'ids-ip':18B 'incomplet':47B,112C 'infrastructur':21B 'inspect':9A,68B,106C 'interrupt':66B,103C 'intrus':30B 'ip':20B 'make':59B 'mishandl':38B 'multipl':69C 'network':23B 'network-secur':22B 'one':55B 'packet':6A,8A,42B,57B,67B,105C,120C,132C 'pars':118C,139C 'product':37B,71C 'remot':49B,89C 'restart':65B,99C,157C 'result':100C,159C 'secur':24B 'send':54B,128C 'sever':35B 'ship':33B 'snort':2A,25B,27B,61B,79C,94C,116C,141C,152C 'success':143C 'target':135C 'teredo':5A,40B,81C,119C,131C 'tunnel':41B 'unauthent':88C 'unexpect':158C 'vulner':76C,108C,126C 'without':51B","nicknames":[],"mitigations":[],"who_affected":"Organizations running Cisco products that include the Snort 3 detection engine with Teredo detection active, where inspection traffic reaches the device from untrusted networks. Teams not running Cisco products with Snort 3 can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-21T17:18:27+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L","cvss_by":"psirt@cisco.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-20197","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-20197","severity":null,"published_at":"2026-10-21T17:18:27+00:00","modified_at":"2026-10-22T14:17:40+00:00","first_seen_at":"2026-10-23T21:57:29+00:00","fetched_at":"2026-10-23T22:29:01+00:00","note":null},{"source":"epss","external_id":"CVE-2026-20197","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-20197","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-24T13:15:54+00:00","fetched_at":"2026-10-24T13:15:54+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"}