CVE-2026-34848: Hoppscotch Stored XSS Vulnerability

CVE-2026-34848 Overview

CVE-2026-34848 is a stored Cross-Site Scripting (XSS) vulnerability affecting Hoppscotch, an open source API development ecosystem. The vulnerability exists in the team member overflow tooltip functionality, where insufficient input sanitization allows malicious JavaScript code to be injected through the display name field. When other users view the team member list and trigger the overflow tooltip, the stored malicious script executes in their browser context.

Critical Impact

Attackers with low-privileged team member access can inject persistent malicious scripts that execute in other users' browsers, potentially leading to session hijacking, credential theft, or unauthorized actions within the Hoppscotch application.

Affected Products

• Hoppscotch versions prior to 2026.3.0

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-34848 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-34848

Vulnerability Analysis

This stored XSS vulnerability resides in the team member overflow tooltip component of Hoppscotch. The application fails to properly sanitize user-supplied display names before rendering them in the tooltip that appears when the team member list overflows. This creates a persistent attack vector where malicious payloads stored in the display name field are executed every time another user triggers the tooltip.

The attack requires low privileges (any authenticated team member can modify their display name) and user interaction (a victim must view the team member tooltip). However, the cross-origin scope change means the attack can affect resources beyond the vulnerable component, potentially impacting confidentiality and integrity of user data.

Root Cause

The root cause is improper neutralization of input during web page generation (CWE-79). The Hoppscotch application does not adequately sanitize or encode special characters in the display name field before rendering it in the team member overflow tooltip. This allows HTML and JavaScript content to be interpreted and executed by the browser rather than displayed as plain text.

Attack Vector

The attack vector is network-based, requiring an authenticated attacker to modify their display name with a malicious XSS payload. The attack flow proceeds as follows:

1. An authenticated team member updates their display name to include malicious JavaScript code
2. The payload is stored in the application database without proper sanitization
3. When another user views the team member list and triggers the overflow tooltip, the malicious script executes
4. The attacker can then steal session tokens, perform actions on behalf of the victim, or redirect users to malicious sites

The vulnerability requires user interaction, as victims must actively trigger the overflow tooltip to execute the payload. See the GitHub Security Advisory GHSA-vw93-4m6p-ccm9 for additional technical details.

Detection Methods for CVE-2026-34848

Indicators of Compromise

• Unusual or suspicious characters in team member display names, particularly HTML tags or JavaScript event handlers
• Browser console errors indicating blocked or executed inline scripts from user-generated content
• Unexpected network requests originating from the Hoppscotch application to external domains
• User reports of unexpected behavior when viewing team member lists

Detection Strategies

• Implement Content Security Policy (CSP) headers and monitor for policy violations that may indicate XSS attempts
• Review audit logs for display name changes containing suspicious patterns such as <script>, onerror, onclick, or javascript: URIs
• Deploy web application firewall (WAF) rules to detect and block common XSS payloads in form submissions
• Monitor for anomalous session activity that may indicate compromised user accounts

Monitoring Recommendations

• Enable verbose logging for user profile modifications and team member management functions
• Set up alerts for CSP violation reports to catch attempted XSS exploitation
• Monitor for unusual authentication patterns that may indicate session token theft
• Review browser developer tools network activity for unexpected external requests when using Hoppscotch

How to Mitigate CVE-2026-34848

Immediate Actions Required

• Upgrade Hoppscotch to version 2026.3.0 or later immediately
• Audit existing team member display names for potentially malicious content and sanitize any suspicious entries
• Implement Content Security Policy headers to provide defense-in-depth against XSS attacks
• Review session logs for any signs of compromise and invalidate suspicious sessions

Patch Information

The vulnerability has been addressed in Hoppscotch version 2026.3.0. Organizations should upgrade to this version or later to remediate the vulnerability. The fix implements proper input sanitization for display names before rendering in the tooltip component.

For detailed information about the patch, refer to the GitHub Release 2026.3.0 and the GitHub Security Advisory GHSA-vw93-4m6p-ccm9.

Workarounds

• If immediate patching is not possible, restrict team member permissions to prevent display name modifications
• Implement server-side input validation to strip HTML tags and JavaScript from display name fields
• Deploy a reverse proxy or WAF with XSS filtering capabilities in front of the Hoppscotch application
• Educate users to avoid triggering team member overflow tooltips until the patch is applied

# Example CSP header configuration for defense-in-depth
# Add to web server configuration (nginx example)
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; connect-src 'self';" always;