Unauthenticated Attackers Can Overflow DD-WRT's UPnP Stack Buffer; CISA's July 24th KEV Mandate for Covered Entities Has Lapsed

Last refreshed2026-09-27

Status: KEV | Advisory ID: CVE-2021-27137

Key Details

CVE	CVE-2021-27137
Vulnerability Name	DD-WRT Stack-Based Buffer Overflow Vulnerability
Affected products	DD-WRT DD-WRT
Exploitation status	Listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating confirmed active exploitation.
Classified as	CWE-121 (Stack-based Buffer Overflow)
KEV listing	Added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2026-07-21.
Exploitation prediction (EPSS)	4.00% probability of exploitation in the next 30 days (90% percentile) -- FIRST.org's EPSS model.
Federal remediation deadline	2026-07-24 (CISA KEV, Binding Operational Directive).

Affected Products, Subsystems & Sectors

Vendor	Product	Affected Versions	Patch Status
DD-WRT	DD-WRT

Vendor

Product

Affected Versions

Patch Status

DD-WRT

Subsystems	General OT
Sectors	Multiple

What to Know

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

Monitor DD-WRT's web page for any future patch releases.

References

Source	Reference
NVD	https://nvd.nist.gov/vuln/detail/CVE-2021-27137
CVE	https://www.cve.org/CVERecord?id=CVE-2021-27137

Source

Reference

NVD

https://nvd.nist.gov/vuln/detail/CVE-2021-27137

CVE

https://www.cve.org/CVERecord?id=CVE-2021-27137

KEV Required Action

Field	Value
KEV Link	https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Date Added to KEV	2026-07-21
Required Action Due Date	2026-07-24
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.

Field

Value

KEV Link

https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Date Added to KEV

2026-07-21

Required Action Due Date

2026-07-24

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.