CVE-2026-3455 in mailparser
Summary
by MITRE • 03/03/2026
Versions of the package mailparser before 3.9.3 are vulnerable to Cross-site Scripting (XSS) via the textToHtml() function due to the improper sanitisation of URLs in the email content. An attacker can execute arbitrary scripts in victim browsers by adding extra quote " to the URL with embedded malicious JavaScript code.
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Analysis
by VulDB Data Team • 03/14/2026
The vulnerability identified as CVE-2026-3455 affects the mailparser package, specifically versions prior to 3.9.3, and represents a critical cross-site scripting vulnerability that exploits improper input sanitization within the textToHtml() function. This flaw resides in the email processing library's handling of URL content within email messages, creating a pathway for malicious actors to inject harmful JavaScript code into email clients. The vulnerability manifests when the package encounters URLs containing embedded malicious payloads, particularly those utilizing additional quote characters that bypass standard sanitization mechanisms. The security implications are severe as this vulnerability allows attackers to execute arbitrary scripts within the context of a victim's browser when processing affected email content.
The technical implementation of this vulnerability stems from inadequate sanitization of URL parameters within the textToHtml() function, which is designed to convert plain text email content into HTML format for display purposes. When the function processes URLs containing JavaScript code, the improper sanitization allows malicious code to persist in the generated HTML output. This flaw directly maps to CWE-79, which defines Cross-site Scripting vulnerabilities as a result of insufficient input validation and output encoding. The vulnerability specifically exploits the lack of proper HTML escaping for URL parameters, allowing attackers to inject script tags or other malicious code that executes when users view the processed email content. The additional quote character mentioned in the vulnerability description serves as a critical bypass mechanism that circumvents standard sanitization checks.
The operational impact of CVE-2026-3455 extends beyond simple script execution, as it provides attackers with potential access to user sessions, data exfiltration capabilities, and phishing opportunities within email environments. Email systems leveraging the vulnerable mailparser package become attack vectors for social engineering campaigns where malicious actors can craft emails that appear legitimate but contain hidden JavaScript payloads. When victims open these emails in browsers, the malicious code executes automatically, potentially leading to credential theft, session hijacking, or redirection to malicious sites. This vulnerability particularly affects web applications that process email content for display, including email clients, ticketing systems, and content management platforms that utilize the mailparser library for email parsing and rendering.
Mitigation strategies for CVE-2026-3455 require immediate upgrade to mailparser version 3.9.3 or later, which includes proper URL sanitization and HTML escaping mechanisms. Organizations should also implement additional defensive measures such as content security policy headers, input validation for all email processing pipelines, and regular security scanning of dependencies. The remediation process must include thorough testing of email processing workflows to ensure that the updated package functions correctly without introducing regressions. Security teams should also monitor for potential exploitation attempts through email traffic analysis and implement network-based detection measures that can identify suspicious URL patterns in email content. From an ATT&CK perspective, this vulnerability aligns with techniques involving client-side exploitation and social engineering, making it critical for organizations to maintain updated security tooling and incident response procedures to address potential exploitation attempts.