CVE-2021-27137DD-WRT Stack-Based Buffer Overflow Vulnerability

BOD 26-04 remediation window

With CISA's SSVC answers for this CVE (automatable: no, technical impact: total), BOD 26-04 Table 1 gives 3 days and forensic triage on a publicly exposed asset (row 3) and 14 days on an asset that is not publicly exposed (row 11) ^S06. CISA set the catalogue due date at 3 days; under BOD 26-04 it reflects CISA's own view of whether the flaw sits on publicly exposed assets ^S07. The directive binds US federal civilian executive branch agencies only.

What CISA says

Short description

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

CWE in the catalogue

CWE-121

Official links

• CISA KEV catalogue entry cisa.gov
• NVD record nvd.nist.gov

Vendor advisory and patch links

References NVD tags Vendor Advisory or Patch, exactly as NVD lists them.

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

Links in CISA's notes

• https://svn.dd-wrt.com/changeset/45724
• https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
• 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

NVD details

CWE (NVD)

CWE-121 by cve@mitre.org

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS versions in NVD

V31

Last modified in NVD

2026-07-22T05:17:07.330

Where each value comes from

This product uses data from the NVD API but is not endorsed or certified by the NVD. CISA does not endorse Sysprobs. Methodology.