CVE-2024-6782: Calibre RCE Vulnerability

CVE-2024-6782 Overview

CVE-2024-6782 is a critical improper access control vulnerability affecting Calibre, the popular open-source e-book management software. This vulnerability allows unauthenticated attackers to achieve remote code execution on systems running vulnerable versions of Calibre's content server feature. The flaw exists in Calibre versions 6.9.0 through 7.14.0, representing a significant attack surface given the software's widespread use for managing and sharing digital book collections.

The vulnerability is classified under CWE-863 (Incorrect Authorization), indicating that the application fails to properly enforce access controls, enabling unauthorized users to execute arbitrary code remotely without authentication.

Critical Impact

Unauthenticated remote code execution allows attackers to fully compromise systems running Calibre's content server, potentially leading to complete system takeover, data theft, and lateral movement within networks.

Affected Products

• Calibre versions 6.9.0 through 7.14.0
• Calibre Content Server deployments exposed to untrusted networks
• Systems running Calibre with network-accessible content sharing features

Discovery Timeline

• 2024-08-06 - CVE-2024-6782 published to NVD
• 2024-08-06 - Last updated in NVD database

Technical Details for CVE-2024-6782

Vulnerability Analysis

This improper access control vulnerability in Calibre stems from inadequate authorization checks in the application's content server component. When Calibre's content server feature is enabled, it exposes web-based functionality for remote e-book management and access. The vulnerability allows unauthenticated attackers to bypass access controls and execute arbitrary code on the target system.

The attack requires no user interaction and can be exploited over the network, making it particularly dangerous for Calibre instances exposed to the internet or untrusted network segments. Successful exploitation grants the attacker the same privileges as the Calibre process, which could include read/write access to the user's e-book library and potentially broader system access depending on deployment configurations.

Root Cause

The root cause of CVE-2024-6782 is improper access control (CWE-863) in Calibre's content server implementation. The application fails to correctly verify that a user is authorized to perform certain operations, allowing unauthenticated attackers to access functionality that should require authentication. This authorization bypass enables attackers to invoke code execution pathways that should be restricted to authenticated administrative users.

Attack Vector

The attack vector for this vulnerability is network-based, targeting Calibre's content server functionality. An attacker can exploit this vulnerability by sending specially crafted requests to a vulnerable Calibre content server instance. The attack does not require any privileges or user interaction, making it highly exploitable in exposed environments.

The vulnerability allows attackers to bypass authentication mechanisms and execute arbitrary code on the server. This could be leveraged to install malware, exfiltrate sensitive data from the e-book library and underlying system, or use the compromised host as a pivot point for further attacks within the network.

Technical details regarding the specific exploitation technique can be found in the Star Labs Security Advisory. The security patch addressing this vulnerability is available in the GitHub commit.

Detection Methods for CVE-2024-6782

Indicators of Compromise

• Unusual network connections to Calibre content server ports (default 8080 or custom configured ports)
• Unexpected process spawning from Calibre parent processes
• Anomalous file system activity in Calibre library directories or system paths
• Unauthorized modifications to Calibre configuration files

Detection Strategies

• Monitor network traffic for suspicious requests to Calibre content server endpoints
• Implement intrusion detection rules to identify exploitation attempts targeting Calibre services
• Deploy endpoint detection and response (EDR) solutions to detect post-exploitation activity such as unexpected child processes
• Audit Calibre server logs for authentication bypass indicators and unusual access patterns

Monitoring Recommendations

• Enable detailed logging for Calibre content server and forward logs to a SIEM solution
• Set up alerts for any unauthorized access attempts or authentication failures
• Monitor for network scanning activity targeting common Calibre server ports
• Track process execution chains originating from Calibre to identify code execution attempts

How to Mitigate CVE-2024-6782

Immediate Actions Required

• Update Calibre to version 7.15.0 or later immediately to patch this vulnerability
• Disable the Calibre content server feature if not required for operations
• Restrict network access to Calibre content server using firewall rules to limit exposure
• Ensure Calibre is not directly exposed to the internet; use VPN or reverse proxy with authentication if remote access is needed

Patch Information

The Calibre development team has addressed this vulnerability in a security update. The fix is available in the GitHub commit 38a1bf50d8cd22052ae59c513816706c6445d5e9. Users should update to Calibre version 7.15.0 or later, which includes the security patch for this improper access control vulnerability.

For detailed technical information about the vulnerability, refer to the Star Labs Security Advisory.

Workarounds

• Disable the Calibre content server entirely if remote access is not needed by not enabling the "Share over the net" feature
• Place the Calibre server behind a reverse proxy that enforces strong authentication before requests reach Calibre
• Use network segmentation to isolate Calibre servers from critical infrastructure and sensitive network segments
• Implement host-based firewall rules to allow connections only from trusted IP addresses

# Example: Restrict Calibre content server access using iptables
# Allow only trusted IP range to access Calibre server on port 8080
iptables -A INPUT -p tcp --dport 8080 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP