CVE-2021-27137 | An issue was discovered in router/upnp/src/ssdp.c in DD-WRT … | CVSS 8.1 HIGH

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).

Metadata

CVE ID: CVE-2021-27137
State: PUBLISHED
Assigner: mitre
Reserved: 2021-02-10 00:00 UTC
Published: 2026-07-16 00:00 UTC
Last updated: 2026-07-22 03:55 UTC
Primary CWE: CWE-121
CWE-121 Stack-based Buffer Overflow
Vendor / Product: DD-WRT / DD-WRT
Sources: cve.org · NVD

Severity & Metrics

8.1 HIGH CVSS 3.1

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

SSVC — CISA Coordinator

Exploitation: ACTIVE
Automatable: no
Tech. Impact: total

CISA Known Exploited Vulnerability

Vulnerability name: DD-WRT Stack-Based Buffer Overflow Vulnerability
Vendor: DD-WRT
Product: DD-WRT
Added to KEV: 2026-07-21
Due date: 2026-07-24
Ransomware: Not known

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.

CISA 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.

Affected products (1)

Vendor	Product	Platform	Versions
DD-WRT	DD-WRT	—	0 < 45724

Weakness (CWE)

CWE	Source	Description
CWE-121	cna	CWE-121 Stack-based Buffer Overflow

CVSS scores (1)

Score	Severity	Version	Source	Vector
8.1	HIGH	3.1	cna	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

References (5)