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CVE-2021-27137

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).

Scores

8.1
CVSS 8.1 out of 10, high severity.
4%
EPSS 4% chance of exploitation in the next 30 days.

The facts

Published
16 July 2026
Last changed
22 July 2026
NVD status
Analyzed
Severity
High, CVSS 8.1 out of 10 (version 3.1)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
Affects
  • dd-wrt dd-wrt
Known exploited
Yes. CISA added it to the Known Exploited Vulnerabilities catalogue on 21 July 2026.
EPSS
4.0% chance of exploitation activity in the next 30 days (percentile 90).

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References