{"id":"CVE-2021-27137","aliases":["EUVD-2021-34854","GHSA-qx3v-2jx6-8m2c"],"status":"published","title":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the...","description":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).","severity":{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.03995,"percentile":0.90664,"model":"v2026.06.15"},"facts":{"in_kev":true,"known_exploited":true,"public_exploit":false,"fix_available":false},"cwes":["CWE-121"],"published":"2026-07-16T00:00:00Z","modified":"2026-07-22T05:17:07Z","kev":{"date_added":"2026-07-21","due_date":"2026-07-24","required_action":"Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.","known_ransomware_use":"Unknown"},"exploitation":[{"source":"euvd","since":"2026-07-21"},{"source":"kev","since":"2026-07-21"}],"products":[{"vendor":"dd-wrt","product":"dd-wrt"},{"vendor":"embedd gmbh","product":"dd-wrt"}],"references":[{"url":"https://svn.dd-wrt.com/changeset/45724","tags":["Patch"]},{"url":"https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/","tags":["exploit","Exploit","Third Party Advisory"]},{"url":"https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo","tags":["Exploit"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137","tags":["government-resource","US Government Resource"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-27137"},{"url":"https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow"},{"url":"https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware"},{"url":"https://github.com/advisories/GHSA-qx3v-2jx6-8m2c"}],"sources":{"cve":[{"id":"CVE-2021-27137","description":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).","status":"published","published":"2026-07-16T00:00:00Z","modified":"2026-07-22T03:55:45.793Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-121"],"updated_at":"2026-11-02T14:33:04.679189Z"}],"euvd":[{"id":"EUVD-2021-34854","description":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).","status":"published","published":"2026-07-16T00:00:00Z","modified":"2026-07-22T03:55:45Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"exploited_since":"2026-07-21","updated_at":"2026-11-02T18:19:46.900828Z"}],"ghsa":[{"id":"GHSA-qx3v-2jx6-8m2c","title":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the...","description":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).","status":"published","published":"2026-07-16T18:31:34Z","modified":"2026-07-21T18:30:50Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"cwes":["CWE-121"],"updated_at":"2026-11-02T15:09:37.555146Z"}],"kev":[{"id":"CVE-2021-27137","title":"DD-WRT Stack-Based Buffer Overflow Vulnerability","description":"DD-WRT contains a stack-based buffer overflow vulnerability that could allow an unauthenticated attacker to overflow an internal buffer used by UPnP and trigger a code execution vulnerability.","cwes":["CWE-121"],"kev":{"date_added":"2026-07-21","due_date":"2026-07-24","required_action":"Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.","known_ransomware_use":"Unknown"},"updated_at":"2026-11-02T17:00:15.999436Z"}],"nvd":[{"id":"CVE-2021-27137","description":"An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).","status":"published","published":"2026-07-16T18:16:39.113Z","modified":"2026-07-22T05:17:07.33Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-121"],"updated_at":"2026-11-02T14:07:09.005706Z"}]}}