{"cve":{"cve_id":"CVE-2021-27137","is_kev":true,"kev_date_added":"2026-07-21","kev_vendor_project":"DD-WRT","kev_product":"DD-WRT","kev_vulnerability_name":"DD-WRT Stack-Based Buffer Overflow Vulnerability","kev_short_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.","kev_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.","kev_due_date":"2026-07-24","kev_known_ransomware":false,"kev_notes":"This vulnerability affects a common open-source component, third-party library, proprietary implementation, or a protocol used by different products. Please check with specific vendors for information on patching status. For more information, please see: https://svn.dd-wrt.com/changeset/45724 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2021-27137","kev_cwes":["CWE-121"],"epss_score":0.03995,"epss_percentile":0.89752,"epss_as_of":"2026-08-26","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).","published_at":"2026-07-16T00:00:00Z","last_modified_at":"2026-07-22T05:17:07.330000Z","cvss_v3_score":8.1,"cvss_v3_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","cvss_v3_severity":"HIGH","cvss_v4_score":null,"cvss_v4_vector":null,"cvss_v4_severity":null,"ssvc_decision":null,"ssvc_exploitation":"active","ssvc_automatable":false,"ssvc_technical_impact":"total","cwes":["CWE-121"],"nvd_references":["https://svn.dd-wrt.com/changeset/45724","https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/","https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html","https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/","https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo"],"vuln_status":"Analyzed","trending_score":null,"is_trending":false,"has_trended":false,"trended_number_one":false,"trending_peak_score":null,"trending_peak_rank":null,"started_trending_at":null,"trended_number_one_at":null,"summary_generated":null,"summary_generated_at":null,"summary_model":null,"created_at":"2026-07-16T18:35:28.564352Z","updated_at":"2026-07-22T22:39:25.137607Z"},"effective_severity":"HIGH","badges":["kev"],"impact_analysis":[],"cvss_v3_decoded":{"version":"3.1","metrics":[{"metric":"AV","name":"Attack Vector","value":"N","value_label":"Network"},{"metric":"AC","name":"Attack Complexity","value":"H","value_label":"High"},{"metric":"PR","name":"Privileges Required","value":"N","value_label":"None"},{"metric":"UI","name":"User Interaction","value":"N","value_label":"None"},{"metric":"S","name":"Scope","value":"U","value_label":"Unchanged"},{"metric":"C","name":"Confidentiality","value":"H","value_label":"High"},{"metric":"I","name":"Integrity","value":"H","value_label":"High"},{"metric":"A","name":"Availability","value":"H","value_label":"High"}]},"cvss_v4_decoded":{"version":null,"metrics":[]},"affected":[{"vendor_slug":"dd-wrt","vendor_name":"DD-WRT","product_slug":"dd-wrt","product_name":"DD-WRT","version_start":"0","version_start_inclusive":true,"version_end":"45724","version_end_inclusive":false,"cpe23_uri":"cve5:dd-wrt:dd-wrt:0:45724"},{"vendor_slug":"dd-wrt","vendor_name":"DD-WRT","product_slug":"dd-wrt","product_name":"DD-WRT","version_start":null,"version_start_inclusive":null,"version_end":"45724","version_end_inclusive":false,"cpe23_uri":"cpe:2.3:o:dd-wrt:dd-wrt:*:*:*:*:*:*:*:*"}],"exploit_refs":[],"news":[],"references":[{"url":"https://svn.dd-wrt.com/changeset/45724","source_type":"MISC","tags":[]},{"url":"https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/","source_type":"MISC","tags":[]},{"url":"https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html","source_type":"MISC","tags":[]},{"url":"https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/","source_type":"MISC","tags":[]},{"url":"https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo","source_type":"MISC","tags":[]}],"timeline":[{"type":"published","at":"2026-07-16T00:00:00Z","label":"CVE published","source":null},{"type":"ssvc_changed","at":"2026-07-16T19:36:28.548654Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-07-16T19:36:28.548654Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-07-16T19:36:28.548654Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"cisa_reported","at":"2026-07-21T00:00:00Z","label":"Added to CISA KEV catalog","source":"kev"},{"type":"ssvc_changed","at":"2026-07-21T16:41:10.176619Z","label":"SSVC decision revised","source":"vulnrichment"}]}