CVE-2022-28820 in ACS Commons
Summary
by MITRE • 04/21/2022
ACS Commons version 5.1.x (and earlier) suffers from a Reflected Cross-site Scripting (XSS) vulnerability in /apps/acs-commons/content/page-compare.html endpoint via the a and b GET parameters. User input submitted via these parameters is not validated or sanitised. An attacker must provide a link to someone with access to AEM Author, and could potentially exploit this vulnerability to inject malicious JavaScript content into vulnerable form fields and execute it within the context of the victim's browser. The exploitation of this issue requires user interaction in order to be successful.
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Analysis
by VulDB Data Team • 04/28/2022
The vulnerability identified as CVE-2022-28820 affects ACS Commons version 5.1.x and earlier installations, representing a critical reflected cross-site scripting flaw within the Adobe Experience Manager (AEM) platform. This security weakness resides in the specific endpoint /apps/acs-commons/content/page-compare.html which processes GET parameters named a and b. The vulnerability stems from inadequate input validation and sanitization mechanisms that fail to properly process user-supplied data, creating an exploitable condition where malicious scripts can be injected and executed within the victim's browser context. The flaw is categorized under CWE-79 as a classic reflected cross-site scripting vulnerability, where attacker-controlled input flows directly into the application's output without proper sanitization.
The technical implementation of this vulnerability allows an attacker to craft malicious URLs containing JavaScript payloads within the a and b parameters, which when accessed by an authenticated AEM Author, will execute the injected code within that user's browser session. This reflected XSS vulnerability requires user interaction to be successfully exploited, meaning that an attacker must somehow convince a legitimate AEM Author to click on a malicious link. The attack vector specifically targets the page comparison functionality, which is commonly used by content authors to compare different versions of web pages. When the vulnerable endpoint processes these parameters, it fails to implement proper output encoding or validation, allowing malicious JavaScript code to be rendered as part of the web page content. This creates a persistent threat where attackers can potentially escalate privileges or extract sensitive information from the authenticated session.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the capability to manipulate the AEM authoring environment and potentially access sensitive content or functionality. Since the vulnerability requires an authenticated user to click on the malicious link, it represents a significant risk in environments where authors have elevated privileges and access to sensitive content management features. Attackers could potentially leverage this vulnerability to steal session cookies, redirect users to malicious sites, or perform actions within the AEM environment that would normally require legitimate author permissions. The exploitation process aligns with ATT&CK technique T1566.001 for initial access through spearphishing with a link, and T1059.001 for command and scripting interpreter execution within the victim's browser context. The vulnerability also demonstrates a failure in the principle of least privilege, as it allows attackers to exploit authenticated sessions without requiring additional authentication mechanisms.
Mitigation strategies for CVE-2022-28820 should focus on immediate patching of affected ACS Commons versions to 5.2.0 or later, which includes proper input validation and sanitization for the affected parameters. Organizations should implement comprehensive input validation at the application level, ensuring that all user-supplied data is properly escaped or encoded before being rendered in web page output. The implementation of Content Security Policy (CSP) headers can provide additional protection against script execution, while regular security testing and code reviews should be conducted to identify similar vulnerabilities in other endpoints. Security awareness training for AEM authors is essential to prevent social engineering attacks that might lead to exploitation, as the vulnerability specifically requires user interaction to be successful. Additionally, network-level protections such as web application firewalls can help detect and block malicious payloads targeting this specific vulnerability, though they should not be considered a substitute for proper code-level fixes. The fix should align with security best practices outlined in OWASP Top 10 2021 category A03: Injection, specifically addressing the need for proper input validation and output encoding to prevent XSS vulnerabilities in web applications.