CVE-2021-27137KEV · OVERDUECWE-121

DD-WRT Stack-Based Buffer Overflow Vulnerability

High · published July 16, 2026

Patch now

Confirmed exploited, and the score agrees

CVSS calls it high at 8.1. It is confirmed in active exploitation. It sits in the 90.5th percentile for exploit probability.

92
days past CISA
deadline
CVSS v3.1
8.1
EPSS
4%
Percentile
90.5
In the wild
Confirmed
What it is

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).

The record
Technical detail
CVSS v3.1
8.1 · HIGH
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.03995 · 90.5th percentile
Weakness
CWE-121 · Stack-based Buffer Overflow
Published
2026-07-16T00:00Z
KEV added
2026-07-21 · due 2026-07-24
EPSS history
Timeline
  • 25 AUG 00:04Z
    EPSS moved 16% → 4%
    epss
  • 21 JUL 00:00Z
    Added to CISA KEV — remediate by Jul 24
    kev
  • 16 JUL 00:00Z
    An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724
    cvelistv5