{"id":"CVE-2026-103411","kind":"vulnerability","aliases":["CVE-2026-103411"],"related":[],"title":"Juniper Session Smart Router: DHCP decoder underflow leaks data, crashes service","description":"An Integer Underflow vulnerability in DhcpMessageDecoder in Juniper Networks Session Smart Router allows an attacker with local network access to cause information disclosure and a denial of service via a malicious DHCP reply.","summary":"An integer underflow in the DHCP message decoder of Juniper Session Smart Router lets a device on the local network send a malicious DHCP reply. The attacker can read information from the router and cause a denial of service.","severity":"high","cvss":7.1,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["adjacent-network","infrastructure","juniper","network-appliance","session-smart-router"],"not_affected_if":[],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-28T17:17:28+00:00","first_seen_at":"2026-10-28T17:34:08+00:00","triaged_at":"2026-10-28T17:34:29+00:00","updated_at":"2026-10-28T17:35:15+00:00","category":"infrastructure","confidence":0.4,"triage":{"at":"2026-10-28T17:34:29Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"network","title":"Juniper Session Smart Router: DHCP decoder underflow leaks data, crashes service","impact":"medium","summary":"An integer underflow in the DHCP message decoder of Juniper Session Smart Router lets a device on the local network send a malicious DHCP reply. The attacker can read information from the router and cause a denial of service.","category":"infrastructure","nicknames":[],"who_cares":["juniper","session-smart-router","network-appliance"],"confidence":0.5,"needs_auth":"unknown","worst_case":"Router leaks memory contents and crashes its DHCP handling","analyst_note":"Find the Juniper advisory for the affected and fixed Session Smart Router releases and whether DHCP client mode is required.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":[],"who_is_affected":"unknown","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000504,"input_tokens":3302,"output_tokens":348,"severity_before":"high"},"analyst_status":"done","analyst_note":"Find the Juniper advisory for the affected and fixed Session Smart Router releases and whether DHCP client mode is required.","search":"'-103411':14A,17A '-2026':13A,16A 'access':87C 'adjac':19B 'adjacent-network':18B 'allow':81C 'applianc':25B 'attack':56B,83C 'caus':64B,89C 'crash':10A 'cve':12A,15A 'data':9A 'decod':6A,37B 'denial':66B,94C 'devic':45B 'dhcp':5A,35B,53B,100C 'dhcpmessagedecod':74C 'disclosur':91C 'inform':59B,90C 'infrastructur':21B 'integ':31B,70C 'junip':1A,22B,39B,76C 'leak':8A 'let':43B 'local':48B,85C 'malici':52B,99C 'messag':36B 'network':20B,24B,49B,77C,86C 'network-appli':23B 'read':58B 'repli':54B,101C 'router':4A,29B,42B,62B,80C 'send':50B 'servic':11A,68B,96C 'session':2A,27B,40B,78C 'session-smart-rout':26B 'smart':3A,28B,41B,79C 'underflow':7A,32B,71C 'via':97C 'vulner':72C","nicknames":[],"mitigations":[],"who_affected":"Session Smart Router deployments where the router acts as a DHCP client on an interface, because the flaw is in the DHCP reply decoder. The attacker must be on the same local network segment as that interface and send a malicious DHCP reply. This is not confirmed from Juniper's advisory yet. Routers that do not use DHCP client mode on any interface are likely unaffected, which also needs vendor confirmation.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T17:17:28+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H","cvss_by":"sirt@juniper.net","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-103411","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-103411","severity":null,"published_at":"2026-10-28T17:17:28+00:00","modified_at":"2026-10-28T17:17:28+00:00","first_seen_at":"2026-10-28T17:34:08+00:00","fetched_at":"2026-10-28T17:34:08+00:00","note":null},{"source":"analyst","external_id":"CVE-2026-103411:964","url":null,"severity":null,"published_at":"2026-10-28T17:35:15+00:00","modified_at":"2026-10-28T17:35:15+00:00","first_seen_at":"2026-10-28T17:35:15+00:00","fetched_at":"2026-10-28T17:35:15+00:00","note":"Juniper's advisory for this CVE is not retrievable yet (CVE published minutes ago; supportportal pages render JS-only, NVD fetch returned nothing). Affected/fixed versions and whether DHCP client mode is required stay unknown; nothing verified. An unconfirmed lead: CERT-FR CERTFR-2026-AVI-1337 cites Juniper JSA112528 (2026-10-16 SSR patch release notice, SSR <7.0.5, 7.1.x <7.1.7, 7.2.x <7.2.3), but it does not name this CVE, so I did not record it as a fix. Revisit when the Juniper JSA appears. NVD gives CVSS 3.1 7.1 AV:A/PR:N, low confidentiality impact, high availability impact, so the attacker has to be on the same L2 segment as the router."}],"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"}