---
id: "CVE-2021-27137"
kind: "vulnerability"
aliases: ["CVE-2021-27137"]
title: "An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724"
severity: "high"
cvss: 8.1
epss: null
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "DD-WRT DD-WRT", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "dd-wrt", "fixed": ["45724"], "affected": "< 45724", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["dd-wrt", "exploited", "infrastructure", "routers", "self-hosted"]
not_affected_if: ["no-dd-wrt-firmware", "upnp-disabled"]
published_at: "2026-07-16T18:16:39+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:51+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-27137", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-27137", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# An issue was discovered in router/upnp/src/ssdp.c in DD-WRT before 45724

DD-WRT router firmware has a stack-based buffer overflow in its UPnP service. An unauthenticated attacker on the network can overflow the buffer and run code on the router.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:DD-WRT DD-WRT affected ? fixed ?
- vendor:dd-wrt affected < 45724 fixed 45724

## Fix

Move to a DD-WRT build that fixes the UPnP overflow, or disable UPnP on the router and restrict the router's LAN and WAN exposure. The sources do not name the fixed version.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-27137
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-27137

## From the sources

DD-WRT contains a stack-based buffer overflow vulnerability that could allow an unauthenticated attacker to overflow an internal buffer used by UPnP and trigger a code execution vulnerability.

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_