CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability
What it is
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.
What to do
Schedule the vendor fix into this week’s change window, prioritising internet-facing and business-critical systems. Confirm the fix is applied everywhere, not just where it was easy.
- Priority
- This week: Schedule into this week’s change window.
- Severity (CVSS)
- 8.1 high
- CISA assessment (SSVC)
- actively exploited; needs manual effort per target; total control of the affected system
- Exploit probability (EPSS, 30 days)
- 4.0%, higher than 90% of all CVEs
- Added to CISA KEV
- 21 July 2026
- CISA fix-by date
- 24 July 2026 (US federal agencies; a sensible deadline for everyone)
- Ransomware use
- Not known
- Weakness
- CWE-121
References
- NIST NVD entry
- CISA KEV entry
- securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killin
- ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
- svn.dd-wrt.com/changeset/45724
- www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-fl
- www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-g
- ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.