A stored cross-site scripting (XSS) vulnerability exists in LightCMS "contents" field

[SKdft]

A stored cross-site scripting (XSS) vulnerability exists in LightCMS that allows an user authorized to upload a malicious .pdf file which acts as a stored XSS payload. If this stored XSS payload is triggered by an administrator it will trigger a XSS attack.

1. login as admin in the article page
   
2. create a new article
   
3. upload the malicious pdf. the content of xss.pdf :

%PDF-1.4
%1111
1 0 obj
<<
/CreationDate (D:20210619104632+08'00')
/Creator (xss)
/Producer (PDF-XChange Core API SDK \(7.0.324.2\))
>>
endobj
2 0 obj
<<
/Metadata 3 0 R
/Pages 4 0 R
/Type /Catalog
>>
endobj
3 0 obj
<<
/Length 2983
/Subtype /XML
/Type /Metadata
>>
stream
<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.5.0">
	<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
		<rdf:Description rdf:about=""
				xmlns:dc="http://purl.org/dc/elements/1.1/"
				xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
				xmlns:xmp="http://ns.adobe.com/xap/1.0/"
				xmlns:pdf="http://ns.adobe.com/pdf/1.3/">
			<dc:format>application/pdf</dc:format>
			<xmpMM:DocumentID>uuid:9c93bc08-8e4e-46cb-b28f-824c693821a4</xmpMM:DocumentID>
			<xmpMM:InstanceID>uuid:2cd63bea-24ca-4ef8-a12c-015da3b28c96</xmpMM:InstanceID>
			<xmp:CreateDate>2021-06-19T10:46:32+08:00</xmp:CreateDate>
			<xmp:CreatorTool>迅捷PDF编辑器 7.0.324.2</xmp:CreatorTool>
			<xmp:ModifyDate>2021-06-19T10:52:02+08:00</xmp:ModifyDate>
			<pdf:Producer>PDF-XChange Core API SDK (7.0.324.2)</pdf:Producer>
		</rdf:Description>
	</rdf:RDF>
</x:xmpmeta>

4. back to content then wo edit this upload:
   
5. when user click the link it will trigger a XSS attack
   

[eddy8]

No better solution have been found except to prohibit users from uploading PDF files, can you give some help to me, thanks.

Adding the “Content-Disposition: Attachment” and “X-Content-Type-Options: nosniff” headers to the response of static files
https://owasp.org/www-community/vulnerabilities/Unrestricted_File_Upload

[SKdft]

reference，we recommend the following：

1. nginx configure the reverse proxy which can add a header to the specified url.

location /{
    if ($request_filename ~* ^.*?.(txt|doc|pdf|rar|gz|zip|docx|exe|xlsx|ppt|pptx)$){
                        add_header Content-Disposition attachment;
                 }
    }

2. if it is possible，refer to
   https://owasp.org/www-community/vulnerabilities/Unrestricted_File_Upload --- It is recommended that this practice be performed for all of the files that users need to download in all the modules that deal with a file download.currently we do this.

3.nginx detects the uploaded pdf and find the xss features such as 'app.alert(....)'.

Hope can help you！