CVE entry · CVE-2021-27137
CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability
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.
- Actively exploited: added to CISA’s KEV catalog on July 21, 2026.
- Use by ransomware: not established so far.
- Remediation deadline for US federal agencies: July 24, 2026.
Description from CISA’s KEV catalog.
What to do
- Check whether your estate includes DD-WRT, including internet-facing devices.
- Apply the vendor’s patch or mitigations (references below). Failing that, isolate the product or stop using it, as CISA requires of US federal agencies.
- An exploited vulnerability has often been used before it was fixed: look for signs of compromise, especially on internet-facing devices.