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CVE-2021-27137

Published: Jul 16, 2026Updated: Jul 22, 2026 Sources: CVE List NVDCWE-121
8.1HIGH
NVD MITRE
EPSS Score
16.5%
Top 3.4%
CISA KEV
Active Exploitation
Since Jul 21, 2026
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
Not available

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).

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:HPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
Open in CVSS calculator →

Weaknesses

CWE-121

Affected Products

DD-WRT
oss-project·DEaka ddwrt
DD-WRTEmbedded
Networking Infrastructure / router-switch
and 1 more affected products View all →

Exploitability

CISA Known Exploited Vulnerability
Added to KEV:Jul 21, 2026
Remediation due:Jul 24, 2026

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.

Official Patch Available
Is your org exposed to CVE-2021-27137?We can run the check for you — a free external exposure review, no install. Check my exposure

Attack Graph

Products CVE Techniques Tactics

Click technique nodes for MITRE ATT&CK details · drag to pan · Ctrl/⌘ + scroll to zoom, or go fullscreen.

MITRE ATT&CK

1 technique
Privilege Escalation
View detailed technique mapping

References

https://svn.dd-wrt.com/changeset/45724
svn.dd-wrt.com
https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
ssd-disclosure.com
https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html
securityaffairs.com
and 3 more references View all →
News mentions
5

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