{"id":"CVE-2021-31755","kind":"vulnerability","aliases":["CVE-2021-31755"],"related":[],"title":"Tenda AC11 Router: Tenda AC11 Router Stack Buffer Overflow Vulnerability","description":"An issue was discovered on Tenda AC11 devices with firmware through 02.03.01.104_CN. A stack buffer overflow vulnerability in /goform/setmac allows attackers to execute arbitrary code on the system via a crafted post request.","summary":"Tenda AC11 router firmware through 02.03.01.104_CN has a stack buffer overflow in the /goform/setmac handler. A remote attacker can send a crafted POST request to run arbitrary code on the device.","severity":"critical","cvss":10.0,"epss":0.86511,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Tenda AC11 Router","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["ac11","exploited","infrastructure","routers","self-hosted","tenda"],"not_affected_if":["default-config"],"how_to_check":"Check the router's firmware version in its admin UI (System Status or similar) and compare it to 02.03.01.104_CN or earlier.","fix":"Update to a firmware release newer than 02.03.01.104_CN from Tenda, or replace the device if no fixed firmware is available.","status":"open","published_at":"2021-05-07T23:15:07+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T20:29:24+00:00","updated_at":"2026-10-23T20:29:24+00:00","category":"infrastructure","confidence":0.85,"triage":{"at":"2026-10-23T20:29:24Z","model":"claude-haiku-5-5","output":{"fix":"Update to a firmware release newer than 02.03.01.104_CN from Tenda, or replace the device if no fixed firmware is available.\nunknown","summary":"Tenda AC11 router firmware through 02.03.01.104_CN has a stack buffer overflow in the /goform/setmac handler. A remote attacker can send a crafted POST request to run arbitrary code on the device.","category":"infrastructure","who_cares":["tenda","ac11","routers","self-hosted"],"confidence":0.85,"analyst_note":"Confirm fixed firmware version and whether Tenda released it, using the NVD entry https://nvd.nist.gov/vuln/detail/CVE-2021-31755 and the KEV catalog listing.","how_to_check":"Check the router's firmware version in its admin UI (System Status or similar) and compare it to 02.03.01.104_CN or earlier.\nunknown","needs_analyst":true,"not_affected_if":["default-config"],"severity_if_unknown":"critical"},"cost_usd":0.000389,"input_tokens":2140,"output_tokens":349,"severity_before":"critical"},"analyst_status":null,"analyst_note":null,"search":"'-2021':12A,15A '-31755':13A,16A '/goform/setmac':42B,79C '02.03.01.104':33B,71C 'ac11':2A,5A,18A,20B,29B,66C 'allow':80C 'arbitrari':55B,84C 'attack':46B,81C 'buffer':8A,38B,75C 'cn':34B,72C 'code':56B,85C 'craft':50B,91C 'cve':11A,14A 'devic':59B,67C 'discov':63C 'execut':83C 'exploit':21B 'firmwar':31B,69C 'handler':43B 'host':26B 'infrastructur':22B 'issu':61C 'overflow':9A,39B,76C 'post':51B,92C 'remot':45B 'request':52B,93C 'router':3A,6A,19A,23B,30B 'run':54B 'self':25B 'self-host':24B 'send':48B 'stack':7A,37B,74C 'system':88C 'tenda':1A,4A,17A,27B,28B,65C 'via':89C 'vulner':10A,77C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-05-07T23:15:07+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvss_by":"nvd@nist.gov","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-31755","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-31755","severity":null,"published_at":"2021-11-03T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T11:39:18+00:00","note":null},{"source":"epss","external_id":"CVE-2021-31755","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-31755","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:43+00:00","fetched_at":"2026-10-23T19:13:43+00:00","note":null},{"source":"nvd","external_id":"CVE-2021-31755","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-31755","severity":null,"published_at":"2021-05-07T23:15:07+00:00","modified_at":"2026-06-17T03:52:12+00:00","first_seen_at":"2026-10-23T19:35:23+00:00","fetched_at":"2026-10-23T19:35:23+00:00","note":null}],"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"}