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CVE-2021-27137

High 8.1 Exploited in the wild (KEV)

Confirmed active exploitation — CISA KEV catalog

Name
DD-WRT Stack-Based Buffer Overflow Vulnerability
Added to catalog
Remediation due date (US federal)
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.

Description

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the UPnP handling functionality allows an unauthenticated remote attacker to send a request that would overflow an internal fixed buffer. Exploitation requires the DD-WRT user to enable UPnP (which is off by default, and only listens on internal interfaces by default). This occurs in ssdp_msearch (reachable by an M-SEARCH request).

Metrics

CVSS 3.1
8.1 (HIGH) Score source: CNA CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS — exploit probability
4% (percentile: 91) as of 1 November 2026
CWE
CWE-121

Affected products

dd-wrt: dd-wrt

References