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CVE-2021-27137

DD-WRT Stack-Based Buffer Overflow Vulnerability

DD-WRT DD-WRT CWE-121

An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 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).

CVSS Score
8.1
High
EPSS — Exploit Probability
4.0%
Riskier than 90% of all CVEs · checked 2026-09-09
Exploitation
Confirmed in the wild
KEV since 2026-07-21
Remediation
Patch available
Federal deadline 2026-07-24
CISA 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. Deadline for federal agencies: 2026-07-24.

NVD entry Vendor patch PoC / advisory CISA KEV

4 articles across 2 outlets · first covered Jun 8, 2026 · latest Jul 22, 2026

Coverage timeline