# CVE-2021-27137

## Summary

- **CVE ID:** CVE-2021-27137
- **Severity:** HIGH
- **CVSS Score:** 8.1 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** CWE-121
- **Published:** Jul 16, 2026
- **Last Modified:** Jul 22, 2026

## 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 Products

- DD-WRT — DD-WRT (0)

## References

- [CNA](https://svn.dd-wrt.com/changeset/45724)
- [CNA](https://ssd-disclosure.com/ssd-advisory-dd-wrt-upnp-buffer-overflow/)
- [CNA](https://securityaffairs.com/193290/uncategorized/iot-botnet-c0xmo-adds-competitor-killing-capability.html)
- [CNA](https://www.bleepingcomputer.com/news/security/c0xmo-botnet-spreads-via-dd-wrt-router-flaw-kills-rival-malware/)
- [CNA](https://www.fortinet.com/blog/threat-research/inside-cross-platform-propagation-of-new-gafgyt-variant-c0xmo)
- [CISA-ADP](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27137)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 4.00%
- **EPSS Percentile:** 89.8

## Known Exploited Vulnerabilities (KEV)

- **Date Added:** Jul 21, 2026
- **Due Date:** Jul 24, 2026

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-09._