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DD-WRT · DD-WRT

CVE-2021-27137

DD-WRT Stack-Based Buffer Overflow Vulnerability

CISA KEV record

CISA date added
2026-07-21
CISA due date
2026-07-24
Known ransomware use
Unknown

NVD risk context

8.1 HIGH

CVSS is a technical severity score. CISA’s KEV status remains the evidence that this vulnerability is known to be exploited.

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Attack vector
Network
The vulnerable service can be reached remotely over a network.
Attack complexity
High
Exploitation depends on conditions outside the attacker’s direct control.
Privileges required
None
The attacker does not need an existing account or privileges.
User interaction
None
No action by another user is required.

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.

NVD reference index

Vendor and remediation references

NVD has tagged these sources as vendor advisories, patches, mitigations, or release notes.

Other NVD references (5)

MITRE CWE context

CWE classification

CWE-121 Stack-based Buffer Overflow

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

View official MITRE CWE details ↗

NVD record timing

NVD record timeline

These dates describe NVD’s record, not CISA’s KEV addition or remediation due date.

NVD published
Jul 16, 2026, 06:16 PM UTC
When NVD first published this CVE record.
NVD last updated
Jul 22, 2026, 05:17 AM UTC
When NVD last changed its analysis or record data.
Advanced: view the technical CVSS vector

This standardized code is intended for security tools and technical analysts. The plain-language risk summary above explains its main points.

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

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CISA 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