What’s Vulnerable › Vulnerabilities

CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: yes — in CISA KEV since 2026-07-21
• EPSS: 4.0% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-16 · updated 2026-07-22
• Weakness: CWE-121

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).

Affected products

• DD-WRT: before 45724 — fixed in 45724

How to fix

Upgrade to a fixed version: DD-WRT 45724. Check the vendor advisory for mitigations.

References

• 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://svn.dd-wrt.com/changeset/45724
• 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
• https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137

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