{"id":"CVE-2026-121617","kind":"vulnerability","aliases":["CVE-2026-121617"],"related":[],"title":"Linksys E5600 router: firmware upload handler lets remote attackers write out of bounds","description":"A security flaw has been discovered in Linksys E5600 1.1.0.26. Affected by this issue is the function init_multipart of the file /cgi-bin/upload_fw.cgi of the component Header Parser. The manipulation results in out-of-bounds write. The attack may be launched remotely. The exploit has been released to the public and may be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way. This vulnerability only affects products that are no longer supported by the maintainer.","summary":"The Linksys E5600 router's firmware upload CGI handler (/cgi-bin/upload_fw.cgi) has an out-of-bounds write in its multipart header parsing. A remote attacker can send a crafted request to corrupt memory on the device, and a public exploit exists.","severity":"high","cvss":7.8,"epss":null,"exploited":false,"exploited_at":null,"products":[{"name":"E5600","fixed":[],"affected":"1.1.0.26","ecosystem":"vendor"}],"ecosystems":[],"tags":["e5600","home-router","infrastructure","iot","linksys"],"not_affected_if":["other-models","unsupported-device-not-used"],"how_to_check":"- Check the router model and firmware version on its admin page; the affected version is `1.1.0.26`.\n- Check whether the router's admin interface is reachable from the internet.","fix":null,"status":"open","published_at":"2026-11-04T03:17:15+00:00","first_seen_at":"2026-11-04T03:46:39+00:00","triaged_at":"2026-11-04T03:47:15+00:00","updated_at":"2026-11-04T03:48:39+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-11-04T03:47:15Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"internet","title":"Linksys E5600 router: firmware upload handler lets remote attackers write out of bounds","impact":"high","summary":"The Linksys E5600 router's firmware upload CGI handler (/cgi-bin/upload_fw.cgi) has an out-of-bounds write in its multipart header parsing. A remote attacker can send a crafted request to corrupt memory on the device, and a public exploit exists.","audience":"everyone","category":"infrastructure","nicknames":[],"who_cares":["linksys","e5600","home-router","iot"],"confidence":0.7,"fix_status":"none","needs_auth":"unknown","worst_case":"remote attacker corrupts router memory and may run code","analyst_note":"Confirm whether authentication is required for /cgi-bin/upload_fw.cgi and whether a vendor or replacement advisory exists; source is NVD only.","how_to_check":"- Check the router model and firmware version on its admin page; the affected version is `1.1.0.26`.\n- Check whether the router's admin interface is reachable from the internet.","plain_action":"If you own a Linksys E5600 router, check its firmware version and keep its admin page off the internet; the vendor no longer supports this model, so a replacement is the practical option.","needs_analyst":true,"not_affected_if":["other-models","unsupported-device-not-used"],"who_is_affected":"Owners of Linksys E5600 routers running firmware 1.1.0.26, where the upload_fw.cgi handler is reachable over the network. The sources say the product is no longer supported by the maintainer and the vendor did not respond, so no fix is expected. Devices not running this model or firmware are not affected.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000728,"input_tokens":4178,"output_tokens":620,"severity_before":"high"},"analyst_status":"done","analyst_note":"Confirm whether authentication is required for /cgi-bin/upload_fw.cgi and whether a vendor or replacement advisory exists; source is NVD only.","search":"'-121617':16A,19A '-2026':15A,18A '/cgi-bin/upload_fw.cgi':37B,91C '1.1.0.26':78C 'affect':79C,144C 'attack':9A,52B,107C,125C 'bound':13A,43B,104C 'cgi':35B 'compon':94C 'contact':129C 'corrupt':59B 'craft':56B 'cve':14A,17A 'devic':63B 'disclosur':133C 'discov':74C 'e5600':2A,20A,21B,30B,77C 'earli':130C 'exist':68B 'exploit':67B,113C 'file':90C 'firmwar':4A,33B 'flaw':71C 'function':85C 'handler':6A,36B 'header':48B,95C 'home':23B 'home-rout':22B 'infrastructur':25B 'init':86C 'iot':26B 'issu':82C 'launch':110C 'let':7A 'linksi':1A,27B,29B,76C 'longer':149C 'maintain':153C 'manipul':98C 'may':108C,121C 'memori':60B 'multipart':47B,87C 'out-of-bound':40B,101C 'pars':49B 'parser':96C 'product':145C 'public':66B,119C 'releas':116C 'remot':8A,51B,111C 'request':57B 'respond':137C 'result':99C 'router':3A,24B,31B 'secur':70C 'send':54B 'support':150C 'upload':5A,34B 'use':123C 'vendor':127C 'vulner':142C 'way':140C 'write':10A,44B,105C","nicknames":[],"mitigations":[],"who_affected":"Owners of Linksys E5600 routers running firmware 1.1.0.26, where the upload_fw.cgi handler is reachable over the network. The sources say the product is no longer supported by the maintainer and the vendor did not respond, so no fix is expected. Devices not running this model or firmware are not affected.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"none","audience":"everyone","plain_action":"If you own a Linksys E5600 router, check its firmware version and keep its admin page off the internet; the vendor no longer supports this model, so a replacement is the practical option.","pkeys":["e5600"],"ptokens":["e5600"],"labels":["e5600","high","homerouter","infrastructure","iot","linksys"],"campaign_type":null,"first_public_at":"2026-11-04T03:17:15+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:P/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":"cna@vuldb.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-121617","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121617","severity":null,"published_at":"2026-11-04T03:17:15+00:00","modified_at":"2026-11-04T03:17:15+00:00","first_seen_at":"2026-11-04T03:46:39+00:00","fetched_at":"2026-11-04T03:46:39+00:00","note":null},{"source":"analyst","external_id":"CVE-2026-121617:1629","url":null,"severity":null,"published_at":"2026-11-04T03:48:39+00:00","modified_at":"2026-11-04T03:48:39+00:00","first_seen_at":"2026-11-04T03:48:39+00:00","fetched_at":"2026-11-04T03:48:39+00:00","note":"Only NVD (VulDB CNA) found; no Linksys advisory, no fix. 1.1.0.26 is the latest release in Linksys's own notes (Dec 2021), so no newer firmware seen. Auth requirement for upload_fw.cgi NOT confirmed: CVSS vector says PR:N but that is the CNA's claim. PoC link not found. Nothing verified; fix status left unconfirmed since no vendor page says no fix."}],"documents":[{"id":63844,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121617","title":"NVD: CVE-2026-121617","kind":"other","source":"analyst","publisher":null,"text":"A security flaw has been discovered in Linksys E5600 1.1.0.26. Function init_multipart of /cgi-bin/upload_fw.cgi (Header Parser) allows out-of-bounds write. Remote attack possible. Exploit public. Vendor contacted early, did not respond. Only affects products no longer supported by the maintainer.","published_at":null,"relation":"describes","confidence":null,"note":null},{"id":63845,"url":"https://downloads.linksys.com/support/assets/releasenotes/E5600_1.1.0.26_Customer_Release_Notes.txt","title":"Linksys E5600 1.1.0.26 release notes (Dec 20, 2021)","kind":"vendor","source":"analyst","publisher":null,"text":null,"published_at":null,"relation":"mentions","confidence":null,"note":null}],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}