CVE-2021-3539 in EspoCRM
Summary
by MITRE • 08/05/2021
EspoCRM 6.1.6 and prior suffers from a persistent (type II) cross-site scripting (XSS) vulnerability in processing user-supplied avatar images. This issue was fixed in version 6.1.7 of the product.
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Analysis
by VulDB Data Team • 05/27/2025
The vulnerability identified as CVE-2021-3539 represents a persistent cross-site scripting flaw classified as type II within EspoCRM version 6.1.6 and earlier installations. This issue specifically manifests in the processing of user-supplied avatar images, creating a significant security risk for organizations utilizing this customer relationship management platform. The vulnerability stems from inadequate input validation and sanitization mechanisms that fail to properly handle malicious payloads embedded within image files uploaded by users. According to CWE-79, this classification indicates a weakness where untrusted data is processed and subsequently rendered in web applications without proper escaping or validation, making it susceptible to XSS attacks that can persist across multiple user sessions.
The technical exploitation of this vulnerability occurs when malicious actors upload specially crafted avatar images containing embedded XSS payloads that are then executed whenever the avatar is displayed within the application interface. This persistent nature means that the malicious code remains active and executable even after the initial upload, affecting all users who view the compromised avatar images. The vulnerability's impact extends beyond simple script execution as it can enable attackers to hijack user sessions, steal sensitive information, perform unauthorized actions on behalf of victims, or redirect users to malicious websites. The flaw essentially transforms the avatar upload functionality into a potential attack vector that can compromise the entire application ecosystem and user data integrity.
From an operational perspective, this vulnerability presents a substantial risk to organizations relying on EspoCRM for business-critical customer relationship management activities. The persistent nature of the XSS vulnerability means that once exploited, malicious code can continue to affect users until the compromised avatar is removed or the application is patched. Attackers could leverage this vulnerability to access sensitive customer data, manipulate CRM records, or escalate privileges within the application. The security implications are particularly concerning given that CRM systems typically contain extensive sensitive information including personal customer data, business communications, and financial records. Organizations may face regulatory compliance violations and reputational damage if such vulnerabilities are exploited successfully.
Mitigation strategies for CVE-2021-3539 primarily involve immediate application of the vendor-provided patch released in version 6.1.7, which addresses the input validation and sanitization issues in avatar image processing. Security teams should implement comprehensive image validation mechanisms that include file type checking, size limitations, and content inspection to prevent malicious payloads from being processed. Network-based security controls such as web application firewalls should be configured to monitor and block suspicious image uploads. Additionally, organizations should conduct regular security assessments of their CRM systems, implement proper access controls, and establish robust incident response procedures. The vulnerability aligns with ATT&CK technique T1566.001 which involves phishing with malicious attachments, as attackers could use this vulnerability to deliver malicious payloads through avatar uploads. Regular security training for users about the risks of uploading untrusted files and implementing principle of least privilege access controls can further reduce the attack surface and potential impact of such vulnerabilities.