CVE-2026-5783: CityPLus Reflected XSS Vulnerability

CVE-2026-5783 Overview

CVE-2026-5783 is a reflected cross-site scripting (XSS) vulnerability in Beyaz Computer Software Design Industry and Trade Ltd. Co. CityPLus. The flaw stems from improper neutralization of user-supplied input during web page generation [CWE-79]. Attackers can craft malicious URLs that execute arbitrary JavaScript in the victim's browser when clicked. The vulnerability affects all CityPLus versions prior to V24.29750.1.0. Exploitation requires user interaction but no authentication, allowing remote attackers to target authenticated CityPLus users via phishing or social engineering. The Turkish national cyber security center (Siber Güvenlik) published advisory TR-26-0263 documenting the issue.

Critical Impact

Successful exploitation enables session hijacking, credential theft, and unauthorized actions in the victim's authenticated CityPLus session, with potential availability impact on the application.

Affected Products

• Beyaz Computer Software CityPLus versions before V24.29750.1.0

Discovery Timeline

• 2026-05-20 - CVE-2026-5783 published to NVD
• 2026-05-20 - Last updated in NVD database

Technical Details for CVE-2026-5783

Vulnerability Analysis

The vulnerability is a reflected XSS flaw in the CityPLus web application. CityPLus fails to sanitize or encode user-controlled input before reflecting it into HTTP responses. When a victim follows an attacker-crafted link, the application echoes attacker-controlled JavaScript into the rendered page. The browser then executes that script under the application's origin.

Reflected XSS bypasses same-origin protections because the malicious payload originates from the trusted CityPLus domain. Attackers can steal session cookies, capture form input, perform actions as the victim, or pivot to further client-side attacks. The attack vector is network-based and requires user interaction, typically through phishing emails or malicious links embedded on third-party sites.

Root Cause

The root cause is improper neutralization of input during web page generation [CWE-79]. CityPLus accepts request parameters and returns them within HTML output without applying contextual output encoding or input validation. Standard mitigations such as HTML entity encoding, JavaScript context escaping, and Content Security Policy (CSP) headers were not enforced in vulnerable versions.

Attack Vector

An attacker constructs a URL containing a malicious script payload in a vulnerable parameter. The attacker delivers the URL to a CityPLus user through email, chat, or a controlled web page. When the user visits the link while authenticated, the embedded script executes in the CityPLus origin. The script can exfiltrate cookies, abuse application APIs, or trigger destructive operations that lead to availability loss.

No verified public proof-of-concept code is available. See the Siber Güvenlik Notification TR-26-0263 for vendor-specific technical details.

Detection Methods for CVE-2026-5783

Indicators of Compromise

• HTTP request logs containing <script>, javascript:, onerror=, or onload= substrings in query parameters directed at CityPLus endpoints
• URL-encoded XSS payloads such as %3Cscript%3E or %3Cimg reflected in CityPLus response bodies
• Outbound requests from user browsers to unfamiliar domains immediately after CityPLus page loads, indicating cookie or token exfiltration

Detection Strategies

• Inspect web server and reverse proxy logs for request parameters containing HTML or JavaScript syntax targeting CityPLus URLs
• Deploy web application firewall (WAF) rules that flag reflected payloads matching OWASP CRS XSS signatures
• Correlate phishing email telemetry with subsequent user clicks on CityPLus links containing encoded script payloads

Monitoring Recommendations

• Enable verbose HTTP access logging on all CityPLus front-end servers and forward logs to a centralized analytics platform
• Monitor authenticated CityPLus session activity for anomalous API calls following inbound clicks from external referrers
• Alert on Content Security Policy violation reports if CSP is deployed in report-only mode during remediation

How to Mitigate CVE-2026-5783

Immediate Actions Required

• Upgrade CityPLus to version V24.29750.1.0 or later as the primary remediation
• Notify CityPLus users of active phishing risk and instruct them to avoid clicking unverified links to the application
• Invalidate active user sessions after patching to revoke any tokens that may have been exposed

Patch Information

Beyaz Computer Software Design Industry and Trade Ltd. Co. addressed the vulnerability in CityPLus V24.29750.1.0. Administrators should consult the Siber Güvenlik Notification TR-26-0263 for vendor coordination details and upgrade guidance.

Workarounds

• Deploy a WAF with reflected XSS signatures in front of CityPLus to block payloads in request parameters until patching completes
• Enforce a strict Content Security Policy that disallows inline scripts and restricts script sources to trusted origins
• Set the HttpOnly and Secure flags on session cookies to limit the impact of successful script execution
• Restrict CityPLus access to trusted networks or VPN users where business requirements permit

# Example WAF rule (ModSecurity) to block reflected script payloads
SecRule ARGS "@rx (?i)(<script|javascript:|onerror=|onload=)" \
    "id:1005783,phase:2,deny,status:403,msg:'CVE-2026-5783 XSS payload blocked'"