Exploited CVEs / CVE-2021-27137
CVE-2021-27137
Updated July 22, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
Actively exploited DD-WRT vulnerability, High severity, CVSS 8.1. Added to the CISA KEV catalog 2026-07-21.
All about CVE-2021-27137: the Senserva AI read, the CISA required action and deadline, the official fix, and the questions admins ask.
DD-WRT Stack-Based Buffer Overflow Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted. Federal agencies were required to remediate by 2026-07-24; treat that date as the outer bound for your own environment. Check the vendor security advisory for the fix.
Risk summary
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Senserva AI Opinion for CVE-2021-27137
This is an unauthenticated stack-based buffer overflow in DD-WRT's UPnP handling that leads to remote code execution on the router itself. DD-WRT is aftermarket router firmware, so exposure is anyone running it on consumer or small-office hardware, particularly where UPnP is enabled and reachable. It sits on CISA KEV as confirmed exploited despite a modest 5% EPSS score, so the router at the network edge is the target.
Do this: Disable UPnP on DD-WRT devices and flash to a patched firmware build, prioritizing any router with UPnP exposed to the WAN.
AI-generated from public data, 2026-07-22. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2021-27137
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for CVE-2021-27137
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
CISA required action
Federal (BOD 22-01) remediation due date: 2026-07-24.
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.
Official fix for CVE-2021-27137
Check the vendor's security advisory channel for the patched DD-WRT versions and workarounds.
Common questions about CVE-2021-27137
Is CVE-2021-27137 actively exploited?
Yes. CVE-2021-27137 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2026-07-21, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 11%.
What is the CISA deadline and required action for CVE-2021-27137?
CISA set the federal (BOD 22-01) remediation due date at 2026-07-24. The verbatim 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.
What fixes CVE-2021-27137?
Check the vendor's security advisory for the patched DD-WRT versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.
Can I ask my own AI about CVE-2021-27137?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2021-27137's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed three times a day (5 AM, 12:30 PM, and 7 PM US Central).
Authoritative references
Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.
