{"id":"CVE-2021-20090","published":"2021-04-29T15:15:10Z","modified":"2026-06-17T03:33:15Z","title":"Arcadyan Buffalo Firmware Path Traversal Vulnerability","vendor":"Arcadyan","product":"Buffalo Firmware","tier":"core","eol":null,"description":{"text":"A path traversal vulnerability in the web interfaces of Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 could allow unauthenticated remote attackers to bypass authentication.","provenance":"source","from":"NVD"},"summary":{"text":"The Buffalo firmware from Arcadyan contains a path traversal flaw in the web interfaces of the WSR-2533DHPL2 and WSR-2533DHP3 routers, where improper limitation of a pathname to a restricted directory exists. An unauthenticated remote attacker with network access can exploit this to bypass authentication, requiring no privileges, no user interaction, and no particular non-default configuration.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-29T13:43:56Z"},"cvss":{"score":9.8,"severity":"CRITICAL","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","provenance":"source","from":"NVD"},"epss":{"score":0.99982,"percentile":0.99982,"date":"2026-10-29","provenance":"source"},"kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","ransomware":false,"requiredAction":"Apply updates per vendor instructions.","notes":"https://nvd.nist.gov/vuln/detail/CVE-2021-20090","provenance":"source"},"vulncheckKev":{"dateAdded":"2021-08-06","exploitedFirstSeen":"2021-08-06","ransomware":false,"evidence":[{"url":"https://blogs.juniper.net/en-us/security/freshly-disclosed-vulnerability-cve-2021-20090-exploited-in-the-wild","date":"2021-08-06"},{"url":"https://www.radware.com/getmedia/18d24c2d-c092-4a61-9ad6-ebb92b7a49b8/Alert_Realtek_SDK.aspx","date":"2021-08-24"},{"url":"https://www.radware.com/getmedia/d312a5fa-2d8d-4c1e-b31e-73046f24bf35/Alert-Dark-OMIGOD.aspx","date":"2021-09-20"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2021-11-03"},{"url":"https://cujo.com/blog/iot-botnet-report-2021-malware-and-vulnerabilities-targeted/","date":"2021-12-17"},{"url":"https://www.cisa.gov/uscert/ncas/alerts/aa22-279a","date":"2022-10-06"},{"url":"https://dashboard.shadowserver.org/statistics/honeypot/vulnerability/map/?day=2024-01-04&host_type=src&vulnerability=cve-2021-20090","date":"2024-01-04"},{"url":"https://dashboard.shadowserver.org/statistics/honeypot/vulnerability/map/?day=2024-03-22&host_type=src&vulnerability=cve-2021-20090","date":"2024-03-22"},{"url":"https://dashboard.shadowserver.org/statistics/honeypot/vulnerability/map/?day=2024-06-10&host_type=src&vulnerability=cve-2021-20090","date":"2024-06-10"},{"url":"https://dashboard.shadowserver.org/statistics/honeypot/vulnerability/map/?day=2024-06-16&host_type=src&vulnerability=cve-2021-20090","date":"2024-06-16"}],"evidenceTotal":26,"provenance":"source"},"exploited":true,"otx":{"pulseCount":50,"pulses":[{"name":"Actively_Exploited_Kev | Oct 29, 2026","url":"https://otx.alienvault.com/pulse/6ae20c1db17e7057ae7d9ad1","created":"2026-10-28"},{"name":"Actively_Exploited_Kev | Oct 28, 2026","url":"https://otx.alienvault.com/pulse/6ae0ba7e0e2a97ff7b218819","created":"2026-10-27"},{"name":"Actively_Exploited_Kev | Oct 27, 2026","url":"https://otx.alienvault.com/pulse/6adf68b85c3e852f3c111d18","created":"2026-10-26"},{"name":"Actively_Exploited_Kev | Oct 24, 2026","url":"https://otx.alienvault.com/pulse/6adb740e397c3ad4799aa4cd","created":"2026-10-23"},{"name":"Actively_Exploited_Kev | Oct 23, 2026","url":"https://otx.alienvault.com/pulse/6ada236fcfba2dfa730ea482","created":"2026-10-22"},{"name":"Actively_Exploited_Kev | Oct 22, 2026","url":"https://otx.alienvault.com/pulse/6ad8d33a077cbb5cab524d80","created":"2026-10-21"},{"name":"Actively_Exploited_Kev | Oct 21, 2026","url":"https://otx.alienvault.com/pulse/6ad78130c4d1ac2be83a8b6d","created":"2026-10-20"},{"name":"Actively_Exploited_Kev | Oct 20, 2026","url":"https://otx.alienvault.com/pulse/6ad62f63c24a405a3423cc13","created":"2026-10-19"},{"name":"Actively_Exploited_Kev | Oct 19, 2026","url":"https://otx.alienvault.com/pulse/6ad4dda174e5797d0bd238b7","created":"2026-10-18"},{"name":"Actively_Exploited_Kev | Oct 18, 2026","url":"https://otx.alienvault.com/pulse/6ad38c22e1848f8189d1c121","created":"2026-10-17"}],"provenance":"machine"},"cwes":[{"id":"CWE-22","name":"Improper Limitation of a Pathname to a Restricted Directory"}],"references":[{"url":"https://www.kb.cert.org/vuls/id/914124","tags":["Third Party Advisory","US Government Resource"]},{"url":"https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.tenable.com/security/research/tra-2021-13","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.kb.cert.org/vuls/id/914124","tags":["Third Party Advisory","US Government Resource"]},{"url":"https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.tenable.com/security/research/tra-2021-13","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20090","tags":["US Government Resource"]}],"techniques":[{"id":"T1190","name":"Exploit Public-Facing Application","tactics":["initial-access"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping","report-passage"],"basisDetail":"claude-haiku-5-5: Exploits exposed web interface via path traversal; keyword query KW:T1190:1","mappingType":"exploitation_technique","evidence":[{"from":"description","quote":"path traversal vulnerability in the web interfaces","start":2,"end":52},{"reportId":"SRC-ab60e18dfb72c1e085c0","quote":"Exploit Public-Facing Application: Exploits vulnerabilities in IoT devices, routers, and servers such as HugeGraph (CVE-2024-27348) and Arcadyan firmware (CVE-2021-20090).","start":19872,"end":20043}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1078","name":"Valid Accounts","tactics":["initial-access","persistence","privilege-escalation","stealth"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Authentication bypass yields valid-access equivalent","mappingType":"primary_impact","evidence":[{"from":"description","quote":"could allow unauthenticated remote attackers to bypass authentication","start":145,"end":214}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"}],"reports":[{"id":"SRC-ab60e18dfb72c1e085c0","title":"Matrix Unleashes A New Widespread DDoS Campaign","publisher":"aquasec.com","url":"https://www.aquasec.com/blog/matrix-unleashes-a-new-widespread-ddos-campaign/","date":"2024-11-26","mentions":[{"quote":"Router Vulnerabilities: Attacks on routers, including ZTE and GPON models, exploit vulnerabilities such as CVE-2017-18368, a command injection flaw, and CVE-2021-20090, which affects various devices running Arcadyan firmware.","start":3779,"end":4004},{"quote":"Exploit Public-Facing Application: Exploits vulnerabilities in IoT devices, routers, and servers such as HugeGraph (CVE-2024-27348) and Arcadyan firmware (CVE-2021-20090).","start":19872,"end":20043}]}],"affected":[],"advisories":[],"euvd":{"id":"EUVD-2021-7547","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-7547","exploited":true,"exploitedSince":"2021-11-03","provenance":"source"},"exploits":[],"exploitSources":{"nuclei":[{"id":"CVE-2021-20090","name":"Buffalo WSR-2533DHPL2 - Path Traversal","severity":"critical","path":"http/cves/2021/CVE-2021-20090.yaml","url":"https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-20090.yaml"}],"provenance":"source"},"detections":{"cveRules":[{"title":"Arcadyan Router Exploitations","id":"f0500377-bc70-425d-ac8c-e956cd906871","level":"critical","status":"test","path":"rules-emerging-threats/2021/Exploits/CVE-2021-20090/web_cve_2021_20090_2021_20091_arcadyan_router_exploit.yml","url":"https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-20090/web_cve_2021_20090_2021_20091_arcadyan_router_exploit.yml","techniques":["T1190"]}]},"exploitRefs":["https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/","https://www.tenable.com/security/research/tra-2021-13"],"flow":[{"stage":"exploitation","techniques":["T1190"],"provenance":"ai"},{"stage":"primary","techniques":["T1078"],"provenance":"ai"}],"timeline":[{"date":"2021-04-29","kind":"published","label":"Published (NVD)","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-20090","provenance":"source"},{"date":"2021-08-06","kind":"exploited-reported","label":"Exploitation first reported (VulnCheck KEV evidence)","url":"https://blogs.juniper.net/en-us/security/freshly-disclosed-vulnerability-cve-2021-20090-exploited-in-the-wild","provenance":"source"},{"date":"2021-11-03","kind":"kev","label":"Added to CISA KEV","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","provenance":"source"},{"date":"2021-11-03","kind":"euvd-exploited","label":"ENISA EUVD: exploited","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-7547","provenance":"source"},{"date":"2024-11-26","kind":"report","label":"Named in aquasec.com: Matrix Unleashes A New Widespread DDoS Campaign","url":"https://www.aquasec.com/blog/matrix-unleashes-a-new-widespread-ddos-campaign/","provenance":"machine"}],"speed":{"daysToPublicExploit":null,"firstExploitFrom":null,"daysToKev":188},"priority":{"score":73.7,"factors":[{"name":"In a KEV catalog","points":35.0,"detail":"listed in CISA KEV and VulnCheck KEV"},{"name":"Recent KEV listing","points":0.0,"detail":"added 1910 days ago"},{"name":"Known ransomware use","points":0.0,"detail":"not known"},{"name":"EPSS percentile","points":20.0,"detail":"percentile 0.9998"},{"name":"Named in threat reports","points":3.87,"detail":"1 report"},{"name":"Public exploit code","points":5.0,"detail":"2 NVD references tagged Exploit; 1 nuclei template"},{"name":"Mentioned in OTX pulses","points":3.0,"detail":"50 pulses"},{"name":"CVSS severity","points":6.86,"detail":"base score 9.8"},{"name":"End-of-life product","points":0.0,"detail":"supported or unknown"}]}}