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

Catalog
2026.09.23
Added
2026-07-21

Answer CVE-2021-27137 is in CISA's Known Exploited Vulnerabilities catalog. It was added on 2026-07-21, and US federal civilian agencies must act on it by 2026-07-24.

DCISA 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.

ARequired 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.

RNotes and references

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

FRecord

CVE
CVE-2021-27137
Vendor
DD-WRT (1 entry in KEV)
Product
DD-WRT (1 entry)
Added to KEV
Federal due date
Past due date (2026-07-24)
Remediation window
3 days
Known ransomware use
Unknown (not confirmed by CISA)

NVD record · CVE.org record

This record repeats CISA's entry and is excluded from search indexes until an analyst note is added.

Source: CISA KEV catalog v2026.09.23, released 2026-09-23. Windows end 2026-09-23.

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