CVE-2021-47854
📋 TL;DR
CVE-2021-47854 is a critical buffer overflow vulnerability in DD-WRT's UPnP service that allows remote attackers to execute arbitrary code on affected routers. Attackers can exploit this by sending specially crafted M-SEARCH packets with oversized UUID payloads. This affects DD-WRT version 45723 installations with UPnP enabled.
💻 Affected Systems
- DD-WRT
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attackers to install persistent malware, pivot to internal networks, intercept traffic, or brick the router.
Likely Case
Router takeover leading to DNS hijacking, credential theft, or use as botnet node for DDoS attacks.
If Mitigated
Limited impact if UPnP is disabled or network segmentation prevents direct access.
🎯 Exploit Status
Exploit code is publicly available on Exploit-DB and other sources, making this easily weaponizable.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 45723
Vendor Advisory: https://dd-wrt.com/
Restart Required: Yes
Instructions:
1. Access DD-WRT web interface. 2. Navigate to Administration > Commands. 3. Run 'nvram set dd_beta=1' then 'nvram commit'. 4. Go to Administration > Firmware Upgrade. 5. Download latest beta from https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/. 6. Flash new firmware and reboot.
🔧 Temporary Workarounds
Disable UPnP Service
linuxDisables the vulnerable UPnP service entirely
nvram set upnp_enable=0
nvram commit
reboot
Block UPnP Ports
linuxBlocks external access to UPnP ports (1900/udp)
iptables -A INPUT -p udp --dport 1900 -j DROP
🧯 If You Can't Patch
- Disable UPnP service immediately via web interface or SSH
- Implement network segmentation to isolate DD-WRT routers from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check DD-WRT version via web interface (Status > Router) or SSH command 'nvram get os_version' - if version is 45723 and UPnP is enabled, device is vulnerable.Check Version:
nvram get os_versionVerify Fix Applied:
Verify version is newer than 45723 and UPnP service is either disabled or patched version is running.📡 Detection & Monitoring
Log Indicators:
- Multiple oversized M-SEARCH packets in router logs
- UPnP service crash entries
Network Indicators:
- Unusual UDP traffic on port 1900 with large payloads
- Multiple M-SEARCH requests from single source
SIEM Query:
source_port:1900 AND packet_size>1000 AND protocol:UDP