{"id":"CVE-2026-120865","kind":"vulnerability","aliases":["CVE-2026-120865"],"related":[],"title":"Citrix NetScaler: HTTP/3 memory overflow can crash or disrupt the gateway","description":"Memory overflow in HTTP/3 (QUIC) can lead to unpredictable or erroneous behavior or Denial of Service in Citrix NetScaler ADC and Citrix NetScaler Gateway.","summary":"A memory overflow in the HTTP/3 (QUIC) handling of Citrix NetScaler ADC and NetScaler Gateway can cause unpredictable behavior or a denial of service. The sources do not say that code execution or data theft is possible.","severity":"high","cvss":8.7,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"NetScaler ADC","fixed":["14.1-73.57"],"affected":"< 14.1-73.57","ecosystem":"vendor"},{"name":"NetScaler Gateway","fixed":["14.1-73.57"],"affected":"< 14.1-73.57","ecosystem":"vendor"}],"ecosystems":[],"tags":["citrix","gateway","http3","infrastructure","netscaler","quic","self-hosted"],"not_affected_if":["http3-disabled","no-http-quic-vserver"],"how_to_check":"In the NetScaler running config look for 'add lb vserver <name> HTTP_QUIC' or 'add cs vserver <name> HTTP_QUIC'. If none exist, the stated precondition is not met. Also confirm the build with 'show version' against: 14.1 < 14.1-73.57, 13.1 < 13.1-64.39, 14.1-FIPS < 14.1-73.58 FIPS, 13.1-FIPS/NDcPP < 13.1-37.293.","fix":"Upgrade to NetScaler ADC/Gateway 14.1-73.57 or later, 13.1-64.39 or later 13.1, ADC 14.1-FIPS 14.1-73.58 FIPS or later, or 13.1-FIPS/NDcPP 13.1-37.293 or later.","status":"open","published_at":"2026-11-13T09:17:34+00:00","first_seen_at":"2026-11-13T09:49:53+00:00","triaged_at":"2026-11-13T09:51:56+00:00","updated_at":"2026-11-13T09:53:34+00:00","category":"infrastructure","confidence":0.85,"triage":{"at":"2026-11-13T09:51:56Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"network","title":"Citrix NetScaler: HTTP/3 memory overflow can crash or disrupt the gateway","impact":"medium","summary":"A memory overflow in the HTTP/3 (QUIC) handling of Citrix NetScaler ADC and NetScaler Gateway can cause unpredictable behavior or a denial of service. The sources do not say that code execution or data theft is possible.","audience":"businesses","category":"infrastructure","nicknames":[],"who_cares":["netscaler","citrix","gateway","http3","quic"],"confidence":0.5,"fix_status":"unknown","needs_auth":"unknown","worst_case":"Gateway process crashes, causing denial of service","analyst_note":"Check the Citrix security bulletin for CVE-2026-120865 for affected versions, fixed builds and whether HTTP/3 must be enabled to be exposed.","how_to_check":"- Check whether HTTP/3 (QUIC) is enabled on the NetScaler ADC or NetScaler Gateway virtual servers\n- Check the running firmware version against the affected ranges in the Citrix advisory\n- unknown for exact commands, as the sources do not give them","plain_action":"","product_name":"","needs_analyst":true,"not_affected_if":["http3-disabled"],"who_is_affected":"NetScaler ADC and NetScaler Gateway deployments that handle HTTP/3 (QUIC) traffic are the exposed systems. Deployments that do not use HTTP/3 may be able to skip it, but the sources do not state this. The sources do not give the affected version ranges.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000749,"input_tokens":4537,"output_tokens":590,"severity_before":"high"},"analyst_status":"done","analyst_note":"Check the Citrix security bulletin for CVE-2026-120865 for affected versions, fixed builds and whether HTTP/3 must be enabled to be exposed.","search":"'-120865':14A,17A '-2026':13A,16A 'adc':19A,42B,87C 'behavior':49B,79C 'caus':47B 'citrix':1A,22B,40B,85C,89C 'code':61B 'crash':7A 'cve':12A,15A 'data':64B 'denial':52B,81C 'disrupt':9A 'erron':78C 'execut':62B 'gateway':11A,21A,23B,45B,91C 'handl':38B 'host':30B 'http/3':3A,36B,71C 'http3':24B 'infrastructur':25B 'lead':74C 'memori':4A,32B,68C 'netscal':2A,26B,41B,44B,86C,90C 'netscaler':18A,20A 'overflow':5A,33B,69C 'possibl':67B 'quic':27B,37B,72C 'say':59B 'self':29B 'self-host':28B 'servic':54B,83C 'sourc':56B 'theft':65B 'unpredict':48B,76C","nicknames":[],"mitigations":[],"who_affected":"Self-managed NetScaler ADC and NetScaler Gateway appliances running a build older than the fixed ones are affected only if they have a load balancing or content switching virtual server of type HTTP_QUIC (HTTP/3). Appliances without such a vserver can skip it for this CVE, though the same bulletin lists many other CVEs. Citrix says the result can be unpredictable behavior or denial of service; it does not state code execution.","tier":"B","verified":{"fix":{"at":"2026-11-13T09:53:34Z","by":"analyst","doc":"https://support.citrix.com/external/article/CTX697305","run_id":3845},"products":{"at":"2026-11-13T09:53:34Z","by":"analyst","doc":"https://support.citrix.com/external/article/CTX697305","run_id":3845},"how_to_check":{"at":"2026-11-13T09:53:34Z","by":"analyst","doc":"https://support.citrix.com/external/article/CTX697305","run_id":3845},"who_affected":{"at":"2026-11-13T09:53:34Z","by":"analyst","doc":"https://support.citrix.com/external/article/CTX697305","run_id":3845}},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":["adc","gateway","netscaleradc","netscalergateway"],"ptokens":["adc","gateway","netscaler"],"labels":["citrix","gateway","high","http3","infrastructure","netscaler","quic","selfhosted"],"campaign_type":null,"search_a":"'-120865':14A,17A '-2026':13A,16A 'adc':19A 'citrix':1A 'crash':7A 'cve':12A,15A 'disrupt':9A 'gateway':11A,21A 'http/3':3A 'memori':4A 'netscal':2A 'netscaler':18A,20A 'overflow':5A","search_b":"'adc':42B 'behavior':49B 'caus':47B 'citrix':22B,40B 'code':61B 'data':64B 'denial':52B 'execut':62B 'gateway':23B,45B 'handl':38B 'host':30B 'http/3':36B 'http3':24B 'infrastructur':25B 'memori':32B 'netscal':26B,41B,44B 'overflow':33B 'possibl':67B 'quic':27B,37B 'say':59B 'self':29B 'self-host':28B 'servic':54B 'sourc':56B 'theft':65B 'unpredict':48B","search_c":"'adc':87C 'behavior':79C 'citrix':85C,89C 'denial':81C 'erron':78C 'gateway':91C 'http/3':71C 'lead':74C 'memori':68C 'netscal':86C,90C 'overflow':69C 'quic':72C 'servic':83C 'unpredict':76C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-11-13T09:17:34+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:L/SI:L/SA:L/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":"50a63c94-1ea7-4568-8c11-eb79e7c5a2b5","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-120865","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-120865","severity":null,"published_at":"2026-11-13T09:17:34+00:00","modified_at":"2026-11-13T09:17:34+00:00","first_seen_at":"2026-11-13T09:49:53+00:00","fetched_at":"2026-11-13T09:49:53+00:00","note":null},{"source":"analyst","external_id":"CVE-2026-120865:3845","url":"https://support.citrix.com/external/article/CTX697305","severity":null,"published_at":"2026-11-13T09:53:34+00:00","modified_at":"2026-11-13T09:53:34+00:00","first_seen_at":"2026-11-13T09:53:34+00:00","fetched_at":"2026-11-13T09:53:34+00:00","note":"Read Citrix bulletin CTX697305: precondition is an LB/CS vserver of type HTTP_QUIC; fixed builds listed; no workaround or exploitation stated. Bulletin check steps read via WebFetch summary. X not searched (not needed, brand-new).","cites":["https://support.citrix.com/external/article/CTX697305"]}],"documents":[{"id":142058,"url":"https://support.citrix.com/external/article/CTX697305","title":"Citrix NetScaler ADC and Gateway Security Bulletin CTX697305","kind":"vendor","source":"analyst","publisher":null,"text":null,"published_at":null,"relation":"advisory","confidence":null,"note":null}],"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"}