Unable to browse a CGI application scripted in PERL: 500-Internal Server Error
Recently I had to troubleshoot a issue where the users were reporting the following error while browsing the site hosted on IIS.
Server Error in Application "DEFAULT WEB SITE/CGI" Internet Information Services 7.5 Error Summary HTTP Error 500.0 - Internal Server Error The page cannot be displayed because an internal server error has occurred. Detailed Error Information
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I captured a FREB trace to determine the entry point of failure. FREB always come in handy during troubleshooting such issues.
Please refer the following link on how to configure FREB: https://learn.iis.net/page.aspx/266/troubleshooting-failed-requests-using-tracing-in-iis
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MODULE_SET_RESPONSE_ERROR_STATUS Warning |
ModuleName="CgiModule", Notification="EXECUTE_REQUEST_HANDLER", HttpStatus="500", HttpReason="Internal Server Error", HttpSubStatus="0", ErrorCode="%1 is not a valid Win32 application. (0x800700c1)", ConfigExceptionInfo="" |
Looking at the above error, I tried changing the application pool bitness, but that didn’t help. I was still stuck with the same error.
IIS was configured as per the following article on IIS.NET: https://www.iis.net/ConfigReference/system.webServer/cgi
We also had an ISAPI and CGI restriction entry for the path where the page was stored on disk.
For e.g: If the page is stored under location: C:\inetpub\wwwroot\CGI\test.cgi, then there would be a entry in applicationhost.config under <isapiCgiRestriction> as shown below:
| <isapiCgiRestriction notListedIsapiisAllowed="false" notListedCgisAllowed="false"> <add path="C:\inetpub\wwwroot\CGI\Test.cgi" allowed="true" description="TEST-CGI" /> </isapiCgiRestriction> |
So the problem was that the page was scripted using PERL. So the above article cannot be used as a reference. Instead we need to download PERL and configure it on the server.
So we downloaded and installed Perl from the below link: https://www.activestate.com/activeperl/downloads
The default installation location is: C:\Perl64. Once installed, we added the handler mapping for .cgi and pointed it to “C:\Perl64\bin\perl.exe” .
Assuming the issue was resolved, I browsed the page again only to be greeted with a different error message.
Server Error in Application "DEFAULT WEB SITE/CGI" Internet Information Services 7.5 Error Summary HTTP Error 502.2 - Bad Gateway The specified CGI application misbehaved by not returning a complete set of HTTP headers. The headers it did return are "". Detailed Error Information
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After researching on this error I found my answer. The handler mapping should be set to: “C:\Perl64\bin\perl.exe "%s" %s”.
Look at the example given below:
| <system.webServer> <handlers accessPolicy="Read, Execute, Script"> <add name="CGI" path="*.cgi" verb="*" modules="CgiModule" scriptProcessor="C:\Perl64\bin\perl.exe “%s” %s" resourceType="Either" requireAccess="Script" /> </handlers> </system.webServer> |
| Note: While adding the script map entry you would be prompted to add a entry in ISAPI and CGI restriction list. When prompted click on the “YES” button. |
More Information:
In the above handler mapping the parameters “%s” %s are case sensitive; they must be in lower-case. If there is a capitalization mismatch. Lets say if they are set to “%S” %S the following error would be seen:
Server Error in Application "DEFAULT WEB SITE/CGI" Internet Information Services 7.5 Error Summary HTTP Error 502.2 - Bad Gateway The specified CGI application misbehaved by not returning a complete set of HTTP headers. The headers it did return are "Can't open perl script "C": No such file or directory ". Detailed Error Information
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You could also refer the following link on how to configure ActivePerl for IIS: https://www.activestate.com/blog/2010/06/setting-iis-activeperl
https://docs.activestate.com/activeperl/5.10/bin/ap-iis-config.html