CVE-2023-6199: Bookstackapp Bookstack SSRF Vulnerability

CVE-2023-6199 Overview

CVE-2023-6199 is a Server-Side Request Forgery (SSRF) vulnerability affecting BookStack version 23.10.2, an open-source wiki platform designed for organizing and storing information. This vulnerability allows authenticated attackers to filter and access local files on the server by exploiting insufficient validation of user-supplied URLs within the application.

Critical Impact

Attackers with low-level privileges can leverage this SSRF vulnerability to access sensitive local files and internal network resources, potentially exposing confidential configuration data, credentials, and internal service information.

Affected Products

• BookStack version 23.10.2
• bookstackapp bookstack

Discovery Timeline

• 2023-11-20 - CVE-2023-6199 published to NVD
• 2025-05-19 - Last updated in NVD database

Technical Details for CVE-2023-6199

Vulnerability Analysis

This Server-Side Request Forgery (SSRF) vulnerability in BookStack version 23.10.2 allows authenticated users to manipulate the application into making requests to arbitrary destinations, including internal network resources and local files on the server. The vulnerability stems from improper validation of user-controlled input that is subsequently used in server-side HTTP requests.

SSRF vulnerabilities like CVE-2023-6199 are particularly dangerous because they allow attackers to bypass network security controls and access resources that would otherwise be inaccessible from external networks. In this case, the vulnerability enables filtering of local files, which could expose sensitive configuration files, credentials, or other protected data stored on the server.

The vulnerability is classified under CWE-918 (Server-Side Request Forgery), which describes scenarios where a web application can be induced to make HTTP requests to arbitrary destinations chosen by the attacker.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and sanitization of URLs provided by users. When BookStack processes certain user-supplied data that includes URLs or file references, it fails to properly validate whether the target destination is safe to access. This allows attackers to craft malicious requests that target internal resources, localhost services, or local file paths that should not be accessible through the application.

Attack Vector

The attack vector for CVE-2023-6199 is network-based, requiring the attacker to have low-level authenticated access to the BookStack application. Once authenticated, an attacker can craft specially formatted requests that trick the server into accessing local files or internal network resources. The attack does not require user interaction and can be executed remotely.

The attacker exploits the SSRF vulnerability by supplying malicious URLs or file path references in application inputs that are processed by the server. The server then makes requests on behalf of the attacker, returning the contents of local files or internal services that would otherwise be protected by network segmentation.

For detailed technical information about the exploitation mechanism, refer to the Fluid Attacks Security Advisory.

Detection Methods for CVE-2023-6199

Indicators of Compromise

• Unusual outbound HTTP requests from the BookStack server to internal IP addresses (e.g., 127.0.0.1, 169.254.x.x, 10.x.x.x, 192.168.x.x)
• Server logs showing access attempts to local file paths through the web application
• Requests containing URL schemes targeting local resources such as file://, gopher://, or dict://
• Anomalous access patterns where authenticated users attempt to access internal services or metadata endpoints

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block SSRF payload patterns in request parameters
• Monitor application logs for requests containing internal IP addresses, localhost references, or file:// URI schemes
• Configure intrusion detection systems (IDS) to alert on outbound connections from web servers to internal network segments
• Review BookStack access logs for suspicious authenticated user activity targeting URL-handling functionality

Monitoring Recommendations

• Enable detailed logging on the BookStack application to capture all URL-related requests and their destinations
• Set up alerts for any outbound connections from the BookStack server to RFC1918 private IP ranges or localhost
• Monitor file access patterns on the server for unusual reads of sensitive configuration files
• Implement network segmentation monitoring to detect lateral movement attempts originating from the web server

How to Mitigate CVE-2023-6199

Immediate Actions Required

• Upgrade BookStack immediately to version 23.10.3 or later, which addresses this SSRF vulnerability
• Review server logs for any indicators of exploitation prior to patching
• Audit user accounts with authenticated access to identify any potentially compromised credentials
• Implement network segmentation to limit the BookStack server's ability to access sensitive internal resources

Patch Information

BookStack has released version 23.10.3 which resolves this SSRF vulnerability. Organizations running BookStack version 23.10.2 should upgrade immediately to the patched version. The official release notes and patch information are available in the BookStack Release v23.10.3 announcement.

Workarounds

• Implement strict egress filtering on the BookStack server to prevent outbound connections to internal network ranges
• Deploy a web application firewall (WAF) with rules to detect and block SSRF attack patterns
• Restrict network access from the BookStack server to only necessary external resources using firewall rules
• Consider placing the BookStack application in a DMZ with limited access to internal network resources until patching is complete

# Example iptables rules to restrict outbound connections from web server
# Block connections to private IP ranges from the BookStack server
iptables -A OUTPUT -d 127.0.0.0/8 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 10.0.0.0/8 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 172.16.0.0/12 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 192.168.0.0/16 -m owner --uid-owner www-data -j DROP
iptables -A OUTPUT -d 169.254.0.0/16 -m owner --uid-owner www-data -j DROP