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CVE-2021-27137

8.1 · HIGHActively Exploited

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724.

Published Jul 16, 2026CWE-121EPSS 4.00%

Overview

CVE-2021-27137 is a high-severity vulnerability. It was published on July 16, 2026 and has a CVSS 3.1 base score of 8.1 (HIGH). This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild.

This vulnerability has a CVSS 3.1 base score of 8.1, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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).

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refsecurityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.htmlRefssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/Refsvn.dd-wrt.com/changeset/45724Refwww.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/Refwww.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmoRefssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/CISAwww.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137

How CyberStrike helps

Frequently asked questions

What is CVE-2021-27137?

CVE-2021-27137 is a high-severity vulnerability. It was published on July 16, 2026 and has a CVSS 3.1 base score of 8.1 (HIGH). This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild.

How severe is CVE-2021-27137?

This vulnerability has a CVSS 3.1 base score of 8.1, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-27137?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-27137?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-27137 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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