22 July 2026
Reference: CVE-2021-27137
1. What is being reported?
The report describes a problem in DD-WRT router software where a programming error in the way it handles certain network requests (UPnP M-SEARCH) can cause a buffer overflow. This means an attacker could send a special request to the router and potentially run harmful code on it without needing to log in.
2. What this means in plain English
If your DD-WRT router has the UPnP feature enabled, it could be vulnerable to hackers who might take control of your router remotely. This could lead to loss of control over your network, data breaches, or interruptions to your internet service.
3. Could this affect a small business?
Small businesses or organisations using DD-WRT routers with UPnP turned on could be affected. If UPnP is off (which is the default setting) and the router is not exposed to the internet, the risk is much lower. If you are unsure whether your router uses DD-WRT or has UPnP enabled, check with your IT provider.
4. What to do now
- Check if your router uses DD-WRT firmware and confirm the version installed.
- Verify whether UPnP is enabled on your router; if it is, consider disabling it immediately.
- Apply any available updates or patches for your DD-WRT router as recommended by the vendor.
- Consult your IT provider to ensure your router is not exposed to the internet or to discuss alternative security measures.
5. Ask your IT provider
Can you confirm if our DD-WRT router is running a vulnerable version and if UPnP is enabled? What steps are being taken to mitigate this security risk?
6. Bottom line
If you use DD-WRT routers, ensure UPnP is disabled or the router is updated to avoid a serious security risk.
Information sourced from CISA KEV, NVD and reputable security reporting.