CVE-2021-27137

DD-WRT · Published July 16, 2026

8.1

CVSS v3.1

HIGH

CISA KEV — Federal agencies must patch by deadline

Actively exploited in the wild

Patch availableGet patch

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).

Affected Products

DD WRT < 45724

CVSS Vector

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