CVE-2021-27137

Summary

CVE	CVE-2021-27137
State	PUBLISHED
Assigner	mitre
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-07-16 18:16:39 UTC
Updated	2026-07-21 19:17:03 UTC
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).

Primary CVSS: v3.1 8.1 HIGH from [email protected]

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

EPSS: 0.108090000 probability, percentile 0.953800000 (date 2026-07-23)

CISA KEV: Listed on 2026-07-21; due 2026-07-24; ransomware use Unknown

Problem Types: CWE-121 | CWE-121 CWE-121 Stack-based Buffer Overflow

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	8.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`
3.1	CNA	CVSS	8.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

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

Vendor	DD-WRT
Product	DD-WRT
Name	DD-WRT Stack-Based Buffer Overflow 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.
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

Type	Vendor	Product	Version	Update	Edition	Language
Operating System	Dd-wrt	Dd-wrt	All	All	All	All

Source	Vendor	Product	Version	Platforms
CNA	DD-WRT	DD-WRT	affected 45724 custom	Not specified

Reference	Source	Link	Tags
www.cisa.gov/known-exploited-vulnerabilities-catalog	134c704f-9b21-4f2e-91b3-4a467353bcc0	www.cisa.gov	US Government Resource
www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new...	[email protected]	www.fortinet.com	Exploit
securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing...	[email protected]	securityaffairs.com	Exploit, Third Party Advisory
www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kil...	[email protected]	www.bleepingcomputer.com	Exploit, Third Party Advisory
ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow	134c704f-9b21-4f2e-91b3-4a467353bcc0	ssd-disclosure.com	Exploit, Third Party Advisory
svn.dd-wrt.com/changeset/45724	[email protected]	svn.dd-wrt.com	Patch
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis
CISA Known Exploited Vulnerabilities catalog	CISA	www.cisa.gov	kev

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.