{"id":"CVE-2026-126401","kind":"vulnerability","aliases":["CVE-2026-126401"],"related":[],"title":"Fleet: unsigned SAML response exhausts server memory and crashes it","description":"Fleet before 4.86.2 contains a denial of service vulnerability that allows unauthenticated attackers to exhaust server memory through quadratic XML canonicalization of unsigned SAML responses. Attackers can send a single crafted SAML response with deeply nested elements declaring new namespace prefixes to POST /api/v1/fleet/sso/callback, crashing the Fleet server.","summary":"Fleet, a device management server, can be crashed by one specially crafted SAML response sent to its SSO callback endpoint. The flaw lets an unauthenticated attacker exhaust server memory, causing a denial of service.","severity":"high","cvss":8.7,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"fleet","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["fleet","other","saml-sso","self-hosted"],"not_affected_if":["fleet-4.86.2-or-later","no-saml-sso"],"how_to_check":"- Check the installed Fleet server version and compare it with `4.86.2`.\n- Look for SSO (SAML) being enabled on the Fleet server, which exposes POST /api/v1/fleet/sso/callback.","fix":"- Fleet versions before `4.86.2` are affected; move to `4.86.2` or later.","status":"open","published_at":"2026-11-13T10:17:44+00:00","first_seen_at":"2026-11-13T10:47:19+00:00","triaged_at":"2026-11-13T10:50:24+00:00","updated_at":"2026-11-13T10:50:24+00:00","category":"other","confidence":0.7,"triage":{"at":"2026-11-13T10:50:24Z","model":"claude-haiku-5-5","output":{"fix":"- Fleet versions before `4.86.2` are affected; move to `4.86.2` or later.","reach":"internet","title":"Fleet: unsigned SAML response exhausts server memory and crashes it","impact":"medium","summary":"Fleet, a device management server, can be crashed by one specially crafted SAML response sent to its SSO callback endpoint. The flaw lets an unauthenticated attacker exhaust server memory, causing a denial of service.","audience":"businesses","category":"other","nicknames":[],"who_cares":["fleet","self-hosted","saml-sso"],"confidence":0.7,"fix_status":"available","needs_auth":"no","worst_case":"Fleet server crashes from memory exhaustion, causing denial of service","analyst_note":"","how_to_check":"- Check the installed Fleet server version and compare it with `4.86.2`.\n- Look for SSO (SAML) being enabled on the Fleet server, which exposes POST /api/v1/fleet/sso/callback.","plain_action":"","product_name":"fleet","needs_analyst":false,"not_affected_if":["fleet-4.86.2-or-later","no-saml-sso"],"who_is_affected":"Teams running a self-hosted Fleet server older than 4.86.2 with SAML single sign-on enabled are exposed, since the vulnerable endpoint is the SSO callback. Fleet instances that do not use SAML SSO, or that run a fixed version, are not affected by the sources' description.","user_interaction":"no","product_ecosystem":"vendor","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.000743,"input_tokens":4626,"output_tokens":560,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-126401':12A,15A '-2026':11A,14A '/api/v1/fleet/sso/callback':102C '4.86.2':61C 'allow':69C 'attack':50B,71C,84C 'callback':43B 'canonic':79C 'caus':54B 'contain':62C 'craft':36B,89C 'crash':9A,32B,103C 'cve':10A,13A 'declar':96C 'deepli':93C 'denial':56B,64C 'devic':27B 'element':95C 'endpoint':44B 'exhaust':5A,51B,73C 'flaw':46B 'fleet':1A,16A,17B,25B,59C,105C 'host':24B 'let':47B 'manag':28B 'memori':7A,53B,75C 'namespac':98C 'nest':94C 'new':97C 'one':34B 'post':101C 'prefix':99C 'quadrat':77C 'respons':4A,38B,83C,91C 'saml':3A,20B,37B,82C,90C 'saml-sso':19B 'self':23B 'self-host':22B 'send':86C 'sent':39B 'server':6A,29B,52B,74C,106C 'servic':58B,66C 'singl':88C 'special':35B 'sso':21B,42B 'unauthent':49B,70C 'unsign':2A,81C 'vulner':67C 'xml':78C","nicknames":[],"mitigations":[],"who_affected":"Teams running a self-hosted Fleet server older than 4.86.2 with SAML single sign-on enabled are exposed, since the vulnerable endpoint is the SSO callback. Fleet instances that do not use SAML SSO, or that run a fixed version, are not affected by the sources' description.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":["fleet"],"ptokens":["fleet"],"labels":["fleet","high","other","samlsso","selfhosted","vendor"],"campaign_type":null,"search_a":"'-126401':12A,15A '-2026':11A,14A 'crash':9A 'cve':10A,13A 'exhaust':5A 'fleet':1A,16A 'memori':7A 'respons':4A 'saml':3A 'server':6A 'unsign':2A","search_b":"'attack':50B 'callback':43B 'caus':54B 'craft':36B 'crash':32B 'denial':56B 'devic':27B 'endpoint':44B 'exhaust':51B 'flaw':46B 'fleet':17B,25B 'host':24B 'let':47B 'manag':28B 'memori':53B 'one':34B 'respons':38B 'saml':20B,37B 'saml-sso':19B 'self':23B 'self-host':22B 'sent':39B 'server':29B,52B 'servic':58B 'special':35B 'sso':21B,42B 'unauthent':49B","search_c":"'/api/v1/fleet/sso/callback':102C '4.86.2':61C 'allow':69C 'attack':71C,84C 'canonic':79C 'contain':62C 'craft':89C 'crash':103C 'declar':96C 'deepli':93C 'denial':64C 'element':95C 'exhaust':73C 'fleet':59C,105C 'memori':75C 'namespac':98C 'nest':94C 'new':97C 'post':101C 'prefix':99C 'quadrat':77C 'respons':83C,91C 'saml':82C,90C 'send':86C 'server':74C,106C 'servic':66C 'singl':88C 'unauthent':70C 'unsign':81C 'vulner':67C 'xml':78C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-10-28T19:34:56+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: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-2026-126401","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-126401","severity":null,"published_at":"2026-11-13T10:17:44+00:00","modified_at":"2026-11-13T10:17:44+00:00","first_seen_at":"2026-11-13T10:47:19+00:00","fetched_at":"2026-11-13T10:47:19+00:00","note":null}],"documents":[{"id":145045,"url":"https://github.com/fleetdm/fleet/security/advisories/GHSA-mjrh-3v6h-8g5p","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-28T19:34:56+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":145046,"url":"https://www.vulncheck.com/advisories/fleet-before-4.86.2-unauthenticated-dos-via-sso-callback-xml-canonicalization","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"}