CVE-2021-27137

Vulnerability details

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.

Added to CISA KEV: 2026-07-21

Ransomware campaign use: Unknown

CISA due date: 2026-07-24

Defensive guidance from CISA

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

This is the source's required-action field, not an independently validated patch procedure. Refer to the vendor for exact affected versions and fixes.