CVE-2026-3106: Teampass Blind XSS Vulnerability

CVE-2026-3106 Overview

A Blind Cross-Site Scripting (XSS) vulnerability has been identified in Teampass, an open-source password manager, affecting versions prior to 3.1.5.16. The vulnerability exists within the password manager's login functionality, specifically in the contraseña parameter of the login form located at index.php. During failed authentication attempts, the application fails to properly sanitize or encode user-supplied input in the username field, allowing arbitrary JavaScript code to be stored and subsequently executed in an administrator's browser when viewing failed login entries.

Critical Impact

Attackers can inject malicious JavaScript that executes in administrator browser sessions when reviewing failed login attempts, potentially leading to session hijacking, credential theft, or complete administrative account compromise.

Affected Products

• Teampass versions prior to 3.1.5.16
• Teampass Password Manager login module
• Teampass administrative interface for viewing login attempts

Discovery Timeline

• 2026-03-31 - CVE-2026-3106 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-3106

Vulnerability Analysis

This Blind XSS vulnerability represents a particularly dangerous class of stored XSS attacks. Unlike traditional reflected XSS where the attacker must trick a victim into clicking a malicious link, blind XSS payloads are stored on the server and executed later when a different user (typically an administrator) views the affected page. In this case, the attack surface is the failed login audit log, which administrators routinely review for security monitoring purposes.

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). The attack can be conducted remotely without authentication, requiring no user interaction from the attacker's perspective—the victim administrator triggers the payload simply by performing their normal administrative duties.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and output encoding within the Teampass login form handler. When processing failed authentication attempts, the application stores the raw, unsanitized username value (the contraseña parameter) directly into the database or log storage. Subsequently, when administrators access the failed login entries through the administrative interface, this stored data is rendered without proper HTML entity encoding or JavaScript escaping, allowing injected script content to execute in the administrator's browser context.

Attack Vector

The attack vector leverages the network-accessible login form as the injection point. An attacker submits specially crafted JavaScript payloads within the username field during intentionally failed login attempts. These malicious payloads are stored by the application and remain dormant until an administrator views the failed login logs. At that point, the injected JavaScript executes within the administrator's authenticated session, providing the attacker with the ability to steal session tokens, modify administrative settings, create backdoor accounts, or exfiltrate sensitive password vault data.

The attack does not require any privileges or prior authentication, and the victim administrator has no indication that viewing routine security logs will trigger malicious code execution. This makes the vulnerability particularly effective for targeted attacks against organizations using Teampass.

Detection Methods for CVE-2026-3106

Indicators of Compromise

• Unusual failed login entries containing HTML tags, script elements, or encoded JavaScript in username fields
• Failed login attempts with usernames containing characters such as <, >, script, onerror, onload, or other event handlers
• Administrative session anomalies following review of failed login audit logs
• Unexpected outbound network connections from administrator workstations after accessing Teampass administrative interfaces

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block XSS payloads in login form submissions
• Monitor for failed login attempts where the username field exceeds typical length or contains suspicious character patterns
• Deploy Content Security Policy (CSP) headers to restrict inline script execution and report violations
• Enable browser-based XSS protection mechanisms and monitor for triggered alerts

Monitoring Recommendations

• Configure logging to capture full request parameters for failed authentication events and analyze for injection attempts
• Set up alerts for failed login entries containing common XSS payload signatures
• Monitor administrator session activity for anomalous behavior following access to audit log pages
• Review Teampass application logs regularly for signs of exploitation attempts

How to Mitigate CVE-2026-3106

Immediate Actions Required

• Upgrade Teampass to version 3.1.5.16 or later immediately
• Review failed login logs for any suspicious entries that may contain JavaScript payloads
• Audit administrator accounts for any unauthorized changes or suspicious activity
• Consider temporarily restricting access to failed login audit functionality until patching is complete

Patch Information

The vulnerability has been addressed in Teampass version 3.1.5.16. Organizations should upgrade to this version or later to remediate the vulnerability. For detailed information about the vulnerability and remediation guidance, refer to the INCIBE Security Notice.

Workarounds

• Implement strict Content Security Policy (CSP) headers that disable inline script execution: script-src 'self'
• Deploy a web application firewall (WAF) with XSS detection rules in front of the Teampass instance
• Restrict administrative interface access to trusted IP ranges only
• Review and sanitize existing failed login log entries before administrators access them

# Example CSP header configuration for Apache
# Add to .htaccess or virtual host configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'none';"

# Example CSP header configuration for Nginx
# Add to server block configuration
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'none';" always;