{"id":"CVE-2026-121290","kind":"vulnerability","aliases":["CVE-2026-121290"],"related":[],"title":"Arista EOS: changing BGP listen port disables default peering protection ACLs","description":"On affected platforms running Arista EOS with Border Gateway Protocol (BGP) changing the BGP listen port from its default value disables default protective Access Control List (ACL) rules against unexpected BGP peering attempts.","summary":"On Arista EOS, changing the BGP listen port from its default value turns off the default access control rules that block unexpected BGP peering attempts. An attacker who can reach the router may be able to establish a BGP peering session it should refuse.","severity":"high","cvss":8.3,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"EOS","fixed":[],"affected":"unknown, see Arista advisory","ecosystem":"vendor"}],"ecosystems":[],"tags":["arista-eos","bgp","infrastructure","network-operators"],"not_affected_if":["default-bgp-port","no-bgp"],"how_to_check":"Exposed only if EOS runs BGP with the BGP listen port changed from its default. Look in the running config under 'router bgp' for a non-default listen port. Affected and fixed EOS versions are unknown until Arista's advisory is published; check the Arista security advisories page for this CVE.","fix":null,"status":"open","published_at":"2026-11-10T20:18:54+00:00","first_seen_at":"2026-11-10T20:46:03+00:00","triaged_at":"2026-11-10T20:47:30+00:00","updated_at":"2026-11-10T20:56:29+00:00","category":"infrastructure","confidence":0.4,"triage":{"at":"2026-11-10T20:47:30Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"network","title":"Arista EOS: changing BGP listen port disables default peering protection ACLs","impact":"high","summary":"On Arista EOS, changing the BGP listen port from its default value turns off the default access control rules that block unexpected BGP peering attempts. An attacker who can reach the router may be able to establish a BGP peering session it should refuse.","audience":"businesses","category":"infrastructure","nicknames":[],"who_cares":["arista-eos","bgp","network-operators"],"confidence":0.5,"fix_status":"unknown","needs_auth":"unknown","worst_case":"Unauthorized BGP peer can inject or manipulate routes","analyst_note":"Find Arista's advisory for CVE-2026-121290 to get affected EOS versions, fixed releases and any workaround; the NVD entry gives only the description and CVSS 8.3.","how_to_check":"unknown","plain_action":"","product_name":"","needs_analyst":true,"not_affected_if":["default-bgp-port","no-bgp"],"who_is_affected":"Organizations running Arista EOS routers or switches that use BGP with a non-default BGP listen port. Devices using the default BGP port keep the protective ACL rules, according to the description. The sources do not name affected versions or a fix.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000692,"input_tokens":4529,"output_tokens":479,"severity_before":"high"},"analyst_status":"done","analyst_note":"Find Arista's advisory for CVE-2026-121290 to get affected EOS versions, fixed releases and any workaround; the NVD entry gives only the description and CVSS 8.3.","search":"'-121290':14A,17A '-2026':13A,16A 'abl':61B 'access':43B,94C 'acl':11A,97C 'affect':72C 'arista':1A,20B,28B,75C 'arista-eo':19B 'attack':53B 'attempt':51B,103C 'bgp':4A,22B,32B,49B,65B,81C,84C,101C 'block':47B 'border':78C 'chang':3A,30B,82C 'control':44B,95C 'cve':12A,15A 'default':8A,37B,42B,89C,92C 'disabl':7A,91C 'eo':2A,21B,29B,76C 'eos':18A 'establish':63B 'gateway':79C 'infrastructur':23B 'list':96C 'listen':5A,33B,85C 'may':59B 'network':25B 'network-oper':24B 'oper':26B 'peer':9A,50B,66B,102C 'platform':73C 'port':6A,34B,86C 'protect':10A,93C 'protocol':80C 'reach':56B 'refus':70B 'router':58B 'rule':45B,98C 'run':74C 'session':67B 'turn':39B 'unexpect':48B,100C 'valu':38B,90C","nicknames":[],"mitigations":[],"who_affected":"Teams running Arista EOS switches or routers with BGP where the BGP listen port has been changed from the default. Per the NVD description, changing it disables the default protective ACL rules against unexpected BGP peering attempts. Devices without BGP or with the default port can skip it. Affected versions and fix are not yet published in a source we could read.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"none","audience":"businesses","plain_action":null,"pkeys":["eos"],"ptokens":["eos"],"labels":["aristaeos","bgp","high","infrastructure","networkoperators"],"campaign_type":null,"search_a":"'-121290':14A,17A '-2026':13A,16A 'acl':11A 'arista':1A 'bgp':4A 'chang':3A 'cve':12A,15A 'default':8A 'disabl':7A 'eo':2A 'eos':18A 'listen':5A 'peer':9A 'port':6A 'protect':10A","search_b":"'abl':61B 'access':43B 'arista':20B,28B 'arista-eo':19B 'attack':53B 'attempt':51B 'bgp':22B,32B,49B,65B 'block':47B 'chang':30B 'control':44B 'default':37B,42B 'eo':21B,29B 'establish':63B 'infrastructur':23B 'listen':33B 'may':59B 'network':25B 'network-oper':24B 'oper':26B 'peer':50B,66B 'port':34B 'reach':56B 'refus':70B 'router':58B 'rule':45B 'session':67B 'turn':39B 'unexpect':48B 'valu':38B","search_c":"'access':94C 'acl':97C 'affect':72C 'arista':75C 'attempt':103C 'bgp':81C,84C,101C 'border':78C 'chang':82C 'control':95C 'default':89C,92C 'disabl':91C 'eo':76C 'gateway':79C 'list':96C 'listen':85C 'peer':102C 'platform':73C 'port':86C 'protect':93C 'protocol':80C 'rule':98C 'run':74C 'unexpect':100C 'valu':90C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-11-10T20:18:54+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/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":"psirt@arista.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-121290","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121290","severity":null,"published_at":"2026-11-10T20:18:54+00:00","modified_at":"2026-11-10T20:18:54+00:00","first_seen_at":"2026-11-10T20:46:03+00:00","fetched_at":"2026-11-10T20:46:03+00:00","note":null},{"source":"analyst","external_id":"CVE-2026-121290:2728","url":null,"severity":null,"published_at":"2026-11-10T20:56:29+00:00","modified_at":"2026-11-10T20:56:29+00:00","first_seen_at":"2026-11-10T20:56:29+00:00","fetched_at":"2026-11-10T20:56:29+00:00","note":"Arista's own advisory for this CVE is not indexed yet (published today); only the NVD description (CNA psirt@arista.com) was found. No versions or fix read, so none stated. Revisit when the advisory appears on arista.com/en/support/advisories-notices."}],"documents":[],"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"}