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.

VendorDD-WRT
ProductDD-WRT
Date added to KEV2026-07-21
Due date (BOD 22-01)2026-07-24
Known ransomware campaign useUnknown
CWECWE-121
Required actionApply 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.

What to do

  1. Identify every instance of DD-WRT DD-WRT in your environment (asset inventory, EDR, vulnerability scanner).
  2. Apply CISA's required action: 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.
  3. Federal civilian agencies must act by 2026-07-24 under BOD 22-01; other organizations can use the same date as a target.
  4. Check the vendor advisory and NVD entry linked below for affected versions, then record the fix in your change log.

Get new KEV entries in your inbox: free n8n workflow. Free CISA KEV Patch Digest (n8n workflow) (Runbook Foundry). A Monday-morning email of KEV entries added in the previous week (Mon-Sun), with your watchlist vendors listed first.
Not affiliated with n8n GmbH or CISA. Not tested on n8n Cloud. n8n is a trademark of n8n GmbH.

Sources

Generated from the CISA feed with AI assistance; facts are taken verbatim from the feed. Not affiliated with or endorsed by CISA. Facts come from the CISA Known Exploited Vulnerabilities catalog (public domain).