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File Upload Bypass at Category Image Leads to RCE

High
thorsten published GHSA-pwh2-fpfr-x5gf Mar 25, 2024

Package

No package listed

Affected versions

3.2.5

Patched versions

3.2.6

Description

Summary

The category image upload function in phpmyfaq is vulnerable to manipulation of the Content-type and lang parameters, allowing attackers to upload malicious files with a .php extension, potentially leading to remote code execution (RCE) on the system.

Details

In the file upload function of the category image, the Content-type can be manipulated to return an empty string for the extension and the lang parameter can be set to .php. to allow an attacker to save a file as .PHP. This allows the uploading of web shells which could lead to RCE on phpmyfaq.

PoC

  1. Generate a fake .GIF file that contains a php command using the tool gifsicle
    a. Cmd: gifsicle < test1.gif --comment "<?php system('whoami'); ?>" > output.php.gif

    image

    b. The contents of the file should look like this:
    image

  2. Browse to “../phpmyfaq/admin/?action=addcategory” and upload the fake .GIF file
    image

  3. Intercept the upload request and modify the params below and forward it:
    3a. lang parameter to .php.
    3b. Content-Type parameter from image/gif to image/gif2

    image

  4. Browse to the “/phpmyfaq/images” directory and notice that our fake .GIF file has been uploaded as a PHP file with the category number as its filename.
    image

  5. Now we just need to browse to “../phpmyfaq/images/category--.php” and see the results of our whoami command. Hence, verifying that RCE is achieved.
    image

Impact

Attackers can upload malicious files containing executable code, allowing them to take control of the vulnerable system. This enables them to execute arbitrary commands, steal sensitive data, disrupt services, and potentially escalate their privileges, posing significant risks to the security and integrity of the system and its data.

Occurrences

In CategoryImage.php line 124, the getimagesize and isValidMimeType functions can be bypassed by uploading a fake .GIF file generated by gifsicle.
image

In CategoryImage.php line 85, the getFileExtension function returns an empty string when the content type doesnt match any of the following 3 mappings. Hence, its possible to just supply an invalid content type such as image/gif2 in step 3 of the PoC to make the function return an empty string.
image

In CategoryImage.php line 66, the getFileName function generate the filename by concatenating the categoryId, categoryName and fileExtension together. This allows us to save the file with a .PHP extension. (It should be possible to just set the payload in step 3 above to just .php but it doesnt work and im not sure why..)
image

Suggested Fix

I believe one of the ways to solve this vulnerability is by forcing the getFileExtension function to return one of the 3 mimetype instead of an empty string. This ensures that the uploaded file will have an image extension and will not execute as a PHP file.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVE ID

CVE-2024-28105

Weaknesses

Credits