CVE-2021-27137

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the...

8.1 HighIn KEV

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).

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: High
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: High

Exploit likelihood

4.00%Down 1.5 points since Jul 17, 2026

What each source reports

CVE List Score used 8.1

Record: CVE-2021-27137
CVSS 3.1: 8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-121
Updated: 2026-11-02

EUVDEUVD-2021-34854 8.1

Record: EUVD-2021-34854
CVSS 3.1: 8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

GitHub AdvisoriesGHSA-qx3v-2jx6-8m2c 8.1

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724. An unsafe strcpy in the...

Record: GHSA-qx3v-2jx6-8m2c
CVSS 3.1: 8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-121
Updated: 2026-11-02

CISA KEV No score

DD-WRT Stack-Based Buffer Overflow Vulnerability

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.

Record: CVE-2021-27137
Weakness: CWE-121
Updated: 2026-11-02

NVD 8.1

Record: CVE-2021-27137
CVSS 3.1: 8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-121
Updated: 2026-11-02

Affected products

History

History
Recorded	Changed	Sources
Nov 3, 2026	exploitation
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, CISA KEV, NVD

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-27137 is a high vulnerability (CVSS 8.1) in Dd-wrt, published July 16, 2026. CISA lists it as known to be exploited, since July 21, 2026. EUVD reports exploitation since July 21, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 4.00%, the 90th percentile. No source names a fixed version.