What is 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).
Timeline
- 2026-07-16Published to the U.S. National Vulnerability Database (NVD)
- 2026-07-21Added to the CISA Known Exploited Vulnerabilities (KEV) catalog
- 2026-07-22NVD record last updated
- 2026-07-24CISA federal remediation deadline (BOD 22-01)
CISA Known Exploited Vulnerability
DD-WRT Stack-Based Buffer Overflow Vulnerability
Affected product
Dd-Wrt
Remediation Steps
- Apply the vendor security update for DD-WRT DD-WRT as a priority.
- Restrict network exposure of the affected service to trusted sources until patched.
- Review logs and detections for indicators of exploitation.
- Confirm fixed versions against the official vendor advisory before deploying.
References
- https://svn.dd-wrt.com/changeset/45724
- https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html
- https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
- https://nvd.nist.gov/vuln/detail/CVE-2021-27137
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 3 of August 2026 (August 17 – 23)
- Vulnerability Priority Report – Week 2 of August 2026 (August 10 – 16)
- Vulnerability Priority Report – Week 1 of August 2026 (August 3 – 9)
- Vulnerability Priority Report – Week 4 of July 2026 (July 27 – August 2)
- Vulnerability Priority Report – Week 3 of July 2026 (July 20 – 26)
Browse all tracked CVEs in the defend.network CVE database →
🤖 This CVE page is generated by defend.network from NVD, CISA KEV, EPSS, and our verified daily briefings. Severity and exploitation data come from official sources; always verify remediation steps against the official vendor advisory before acting in production.