Buffer overflow in Dd-Wrt
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).
Vulnerability class: Buffer Overflow
EPSS: 0.040 (89.8th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
Affected products
- Dd-wrt — versions 0
Weakness classification (CWE)
CISA KEV (Known Exploited Vulnerabilities)
This CVE is on the CISA KEV catalog, added on . CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.
BOD 22-01 due date: .
Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Public proof-of-concept exploits
References
- cve@mitre.org (Patch)
- cve@mitre.org (Exploit, Third Party Advisory)
- cve@mitre.org (Exploit, Third Party Advisory)
- cve@mitre.org (Exploit, Third Party Advisory)
- cve@mitre.org (Exploit)
- 134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)
Frequently asked questions
- What is CVE-2021-27137?
- CVE-2021-27137 is a high-severity vulnerability in Dd-Wrt, classified under Stack-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-07-16.
- How severe is CVE-2021-27137?
- High severity. CVSS v3 base score is 8.1 out of 10.
- Is CVE-2021-27137 known to be exploited?
- Yes. CVE-2021-27137 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-07-21), indicating it is being actively exploited. 9 public proof-of-concept repositories are indexed.