CVE-2019-9595 in AppCMS
Summary
by MITRE
AppCMS 2.0.101 allows XSS via the upload/callback.php params parameter.
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Analysis
by VulDB Data Team • 07/26/2023
The vulnerability identified as CVE-2019-9595 affects AppCMS version 2.0.101 and represents a cross-site scripting vulnerability that arises from improper input validation within the upload/callback.php endpoint. This flaw specifically targets the params parameter, which is processed without adequate sanitization or encoding mechanisms. The vulnerability exists within the content management system's file upload functionality, where user-supplied parameters are directly incorporated into the application's response without proper security controls. The affected component operates as part of the CMS's callback handling mechanism, which typically manages asynchronous operations following file uploads or other user interactions. This particular implementation fails to validate or sanitize the params parameter, creating an opportunity for malicious actors to inject malicious scripts that can execute within the context of other users' browsers. The vulnerability is classified under CWE-79 as Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly escape or encode user-controllable data before it is rendered in web pages. This weakness directly enables attackers to perform XSS attacks that can compromise user sessions, steal sensitive information, or redirect users to malicious sites. The attack vector is particularly concerning as it leverages the legitimate upload functionality of the CMS, making it more difficult to detect and prevent through traditional security measures. The operational impact extends beyond simple script execution, as successful exploitation can lead to complete session hijacking, data exfiltration, and potential privilege escalation within the CMS environment.
The technical exploitation of this vulnerability requires an attacker to craft a malicious payload that includes script code within the params parameter of the upload/callback.php endpoint. When the CMS processes this parameter without proper validation, the injected scripts become part of the response sent to the victim's browser, where they execute in the context of the authenticated user's session. This type of vulnerability is particularly dangerous because it can be exploited through various means including social engineering attacks where users are tricked into uploading files with malicious parameters or through automated scanning tools that identify the vulnerable endpoint. The vulnerability demonstrates a critical flaw in the application's security architecture where input validation is not consistently applied across all parameters, particularly those used in callback mechanisms that are often assumed to be safe due to their legitimate use cases. The attack can be executed against any user who accesses the vulnerable page or interacts with the CMS functionality that processes the callback parameters. This vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript, as it enables attackers to execute malicious JavaScript code within victim browsers. The flaw also relates to T1566.001 for Initial Access: Phishing, since attackers can craft phishing emails or social engineering campaigns that leverage this vulnerability to deliver malicious payloads.
The remediation and mitigation strategies for CVE-2019-9595 must address the fundamental issue of inadequate input validation within the upload/callback.php endpoint. Organizations should implement comprehensive parameter sanitization that removes or encodes potentially dangerous characters before processing user input. This includes applying strict input validation rules that reject or sanitize any data containing script tags, event handlers, or other potentially malicious constructs. The fix should involve implementing proper output encoding mechanisms that ensure any user-controllable data is properly escaped before being rendered in web responses. Security patches should be applied immediately to upgrade AppCMS to a version that addresses this vulnerability, as the flaw exists in version 2.0.101 and likely affects other versions within the same release cycle. Organizations should also implement web application firewalls that can detect and block malicious payloads targeting this specific vulnerability pattern. Additional defensive measures include implementing content security policies that restrict script execution and monitoring for unusual patterns in upload activities. Regular security testing and code reviews should be conducted to identify similar input validation flaws in other parts of the application. The vulnerability serves as a reminder of the importance of applying security controls consistently throughout all application components, particularly those handling user-supplied data in callback or asynchronous processing functions. Organizations should also consider implementing automated vulnerability scanning tools that can detect similar XSS vulnerabilities across their entire application portfolio, as this type of flaw is commonly found in CMS platforms and web applications that fail to properly validate user input across all request parameters. The remediation process should include thorough testing to ensure that the fix does not break legitimate functionality while effectively preventing the XSS attack vector.