CVE-2026-2813

Executive Summary

CVE-2026-2813 is a client-side open redirect vulnerability in Esri ArcGIS Server version 11.5. The flaw resides in the login redirection workflow, where insufficient input validation allows an authenticated attacker to craft a malicious request that redirects the user’s browser to an untrusted external site. This is a low-severity issue (CVSS 4.7) with limited confidentiality impact, requiring user interaction and authentication. No server-side compromise or cross-component impact is possible. The vulnerability is confined to the same security boundary and affects only the client-side navigation logic during authentication.

Supply Chain & Package Security

This vulnerability is not related to an open-source package (NPM, PyPI, Go, Ruby). It affects a proprietary enterprise GIS server product from Esri. No supply chain or package security implications are present.

CVSS Breakdown & Threat Level

• CVSS Score: 4.7 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Authenticated)
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: None
• Availability Impact: None

Threat Level: Low. Exploitation requires authentication and user interaction, and the impact is limited to a client-side redirect with no server compromise.

Deep Dive & Mechanics

The vulnerability exists in the login redirection workflow of ArcGIS Server. When a user authenticates, the server may redirect the browser to a URL specified in a parameter (e.g., redirect or returnUrl). Due to insufficient input validation, an authenticated attacker can craft a specially crafted request that includes a malicious external URL. If a victim user clicks on the crafted link or is tricked into interacting with it, the browser will be redirected to the attacker-controlled site.

Key Technical Details:

• The flaw is in the client-side navigation logic, not server-side processing.
• The attacker must be authenticated to the ArcGIS Server instance.
• The redirect occurs only during the authentication flow.
• No server-side data is exposed or compromised.
• The vulnerability is limited to the same security boundary (no cross-component impact).

Attack Flow:

1. Attacker authenticates to ArcGIS Server.
2. Attacker crafts a URL with a malicious redirect parameter (e.g., https://victim-arcgis-server.com/login?redirect=https://evil.com).
3. Attacker sends the crafted URL to a victim (e.g., via phishing email).
4. Victim clicks the link and is redirected to the attacker’s site after authentication.
5. The attacker can then perform phishing or other social engineering attacks.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The vulnerable code likely accepts a redirect parameter without proper validation:

// Vulnerable: No validation of redirect URL
function handleLoginRedirect(redirectUrl) {
    window.location.href = redirectUrl;
}

Patched Code (Conceptual): The patched code should validate the redirect URL against a whitelist of allowed domains:

// Patched: Validate redirect URL against allowed domains
const allowedDomains = ['example.com', 'arcgis-server.com'];
function handleLoginRedirect(redirectUrl) {
    try {
        const url = new URL(redirectUrl);
        if (allowedDomains.includes(url.hostname)) {
            window.location.href = redirectUrl;
        } else {
            // Redirect to default page
            window.location.href = '/default';
        }
    } catch (e) {
        // Invalid URL, redirect to default
        window.location.href = '/default';
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Access to an ArcGIS Server 11.5 instance with valid credentials.
• A victim user who will click the crafted link.

Exploitation Steps:

1. Identify the login endpoint (e.g., https://target-arcgis-server.com/login).
2. Craft a malicious URL with a redirect parameter pointing to an attacker-controlled site:

   https://target-arcgis-server.com/login?redirect=https://attacker.com/phishing
   

3. Send the crafted URL to the victim via email or other means.
4. When the victim clicks the link and authenticates, they will be redirected to the attacker’s site.

No exploit code is available from Exploit-DB or other sources.

Blue Team (Detection & Mitigation)

Detection:

• Monitor for unusual login redirect parameters in web logs.
• Look for requests to /login with redirect parameters pointing to external domains.
• Use web application firewalls (WAF) to block redirects to untrusted domains.

Mitigation:

• Apply the vendor patch when available.
• Implement strict input validation on the redirect parameter.
• Use a whitelist of allowed redirect destinations.
• Educate users about phishing attacks that exploit open redirects.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /login with redirect parameter containing external domains.
  • Unusual referrer headers pointing to external sites after authentication.
• Log IOCs:
  • Web server logs showing redirect parameter with non-standard URLs.
  • Authentication logs with unusual redirect patterns.
• File IOCs:
  • No specific file-based IOCs.

Detection Engineering

YARA Rule

rule CVE_2026_2813_ArcGIS_Open_Redirect {
    meta:
        description = "Detects potential exploitation of CVE-2026-2813 in ArcGIS Server logs"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-2813"
    strings:
        $redirect_param = /redirect=https?:\/\/[^\/]+\.[^\/]+/ nocase
        $login_path = "/login" nocase
    condition:
        $login_path and $redirect_param
}

Sigma Rule

title: ArcGIS Server Open Redirect Exploitation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2026-2813 open redirect in ArcGIS Server
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
    service: http
detection:
    selection:
        cs-uri-query|contains: "/login?redirect=http"
    condition: selection
falsepositives:
    - Legitimate redirects to internal domains
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-2813 ArcGIS Server Open Redirect Attempt"; flow:to_server; content:"/login"; http_uri; content:"redirect"; http_uri; pcre:"/redirect=https?:\/\/[^\/]+\.[^\/]+/Ui"; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade ArcGIS Server to a patched version when available (currently no patch).
2. Implement input validation on the redirect parameter to only allow internal domains.
3. Use a web application firewall (WAF) to block redirects to external domains.
4. Monitor logs for suspicious redirect patterns.

Long-term Recommendations:

• Apply vendor patches as soon as they are released.
• Conduct regular security assessments of ArcGIS Server configurations.
• Educate users about phishing attacks that exploit open redirects.
• Implement strict URL validation for all redirect parameters.

Workarounds:

• Disable the redirect functionality if not needed.
• Use a reverse proxy to filter out malicious redirect parameters.

Valters IT