# CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability

> CVE-2021-27137: DD-WRT Stack-Based Buffer Overflow Vulnerability. CVSS 8.1 (CVSS 3.1), in CISA KEV.

Canonical: https://rewindex.com/cve/CVE-2021-27137
Last updated: 2026-07-22T05:17:07Z

- Published: 2026-07-16 00:00 UTC · Updated: 2026-07-22 05:17 UTC · Assigner: mitre
- CVSS: 8.1 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS: 4.0%, 90th percentile (scored 2026-10-25)
- CISA KEV: yes, added 2026-07-21, federal due date 2026-07-24, ransomware use: Unknown
- CWE: CWE-121

## 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).

## CISA 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.

## Affected vendors and products

- DD-WRT: DD-WRT

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-27137)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2021-27137)
- [https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html](https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html)
- [https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/](https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/)
- [https://svn.dd-wrt.com/changeset/45724](https://svn.dd-wrt.com/changeset/45724)
- [https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/](https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/)
- [https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo](https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2021-27137 · Markdown: https://rewindex.com/cve/CVE-2021-27137.md · JSON: https://rewindex.com/api/v1/cves/CVE-2021-27137 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:12:19.539Z