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.

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This report contains official claims from a government or institutional source and may not be independently verified.

Threat HighOfficial ClaimGovernmentConf ConfirmedUnited States · North AmericaPublishedCISA

Original publisher

CISA

Original source URL

https://svn.dd-wrt.com/changeset/45724

Source country

United States

Reporting region

North America

Language

Institution

CISA

Published (UTC)

Jul 21, 2026, 12:00 AM

Ingested (UTC)

Jul 21, 2026, 11:42 PM

Verification

Official Claim

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CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability
Vendor/project: DD-WRT
Product: DD-WRT
Date added to KEV: 2026-07-21
Due date: 2026-07-24
Known ransomware use: Unknown
CWEs: CWE-121
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.

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.

Notes:
This vulnerability affects a common open-source component, third-party library, proprietary implementation, or a protocol used by different products. Please check with specific vendors for information on patching status. For more information, please see: https://svn.dd-wrt.com/changeset/45724 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2021-27137
CISA KEV catalog entry for CVE-2021-27137
Original source: https://svn.dd-wrt.com/changeset/45724

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