CVE-2021-27137
Act now ● On CISA KEV — actively exploited
Actively exploited — on the CISA KEV list.
CVSS base
8.1
HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS — probability of exploitation (30 days)
4.0%
90.0th percentile
CISA KEV
Listed
Added 2026-07-21 · patch by 2026-07-24
Weakness / dates
CWE-121
Published 2026-07-16 · modified 2026-07-22
CVSS breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
| Attack Vector | N | Network |
| Attack Complexity | H | High |
| Privileges Required | N | None |
| User Interaction | N | None |
| Scope | U | Unchanged |
| Confidentiality | H | High |
| Integrity | H | High |
| Availability | H | High |
Timeline
- 2026-07-16 — Published (NVD)
- 2026-07-21 — Added to CISA KEV (actively exploited)
- 2026-07-24 — CISA patch-by deadline
- 2026-07-22 — Last modified (NVD)
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
References
- exploit https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html
- exploit https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
- https://svn.dd-wrt.com/changeset/45724
- exploit https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/
- exploit https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo
- exploit https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137