CVE-2021-27137

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).

• CWE-121

• https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.htmlExploit, Third Party Advisory
• https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/Exploit, Third Party Advisory
• https://svn.dd-wrt.com/changeset/45724Patch
• https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/Exploit, Third Party Advisory
• https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmoExploit
• https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/Exploit, Third Party Advisory
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137US Government Resource

Published

Jul 16, 2026

Last Modified

Jul 22, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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