Exploitation Summary
CVE-2021-27137 is actively exploited and listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added July 21, 2026.
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).
References (6)
Core 6
Core References
Third Party Advisory, US Government Resource
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137
Scores
CVSS v3
8.1
EPSS
0.0545
EPSS Percentile
91.9%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CISA SSVC
Vulnrichment
Exploitation
active
Automatable
no
Technical Impact
total
Details
CISA KEV
2026-07-21
VulnCheck KEV
2026-06-03
ENISA EUVD
EUVD-2021-34854
CWE
CWE-121
Status
published
Products (1)
DD-WRT/DD-WRT
< 45724
Published
Jul 16, 2026
KEV Added
Jul 21, 2026
Tracked Since
Jul 16, 2026