CVE-2023-24487: Citrix ADC Information Disclosure Flaw

CVE-2023-24487 Overview

CVE-2023-24487 is an arbitrary file read vulnerability affecting Citrix Application Delivery Controller (ADC) and Citrix Gateway. This vulnerability allows unauthenticated remote attackers to read arbitrary files from the affected systems over the network. Given the critical nature of Citrix ADC and Gateway appliances in enterprise network infrastructure—serving as the primary entry points for remote access and application delivery—this vulnerability poses significant risk to organizations relying on these products.

Critical Impact

Unauthenticated attackers can remotely read arbitrary files from Citrix ADC and Gateway appliances, potentially exposing sensitive configuration data, credentials, and other confidential information without any user interaction required.

Affected Products

• Citrix Application Delivery Controller (ADC) - Standard, FIPS, and NDCPP editions
• Citrix Gateway
• Citrix ADC across multiple version branches

Discovery Timeline

• July 10, 2023 - CVE-2023-24487 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-24487

Vulnerability Analysis

This arbitrary file read vulnerability stems from improper handling of check function return values (CWE-253), allowing attackers to access files outside of intended directories on the affected Citrix appliances. The vulnerability can be exploited remotely without authentication, requiring no user interaction. The exploitation results in a high impact to confidentiality, as attackers can read sensitive files containing configuration data, certificates, credentials, and other sensitive information stored on the appliance.

The vulnerability is particularly concerning because Citrix ADC and Gateway appliances often store sensitive authentication credentials, SSL certificates, and network configuration data that could be leveraged for further attacks against the organization's infrastructure.

Root Cause

The root cause of CVE-2023-24487 relates to improper handling of check function return values (CWE-253). When certain security checks are performed on file access operations, the return values from these check functions are not properly validated or handled. This allows attackers to bypass intended access restrictions and read files outside of designated directories.

This type of vulnerability typically occurs when developers fail to properly verify that security-critical functions have succeeded before proceeding with file operations, creating a gap that attackers can exploit to access unauthorized resources.

Attack Vector

The attack is conducted over the network against vulnerable Citrix ADC or Gateway appliances. An unauthenticated attacker can craft malicious requests that exploit the improper return value checking to read arbitrary files from the target system. The attack requires:

• Network access to the vulnerable Citrix appliance
• No authentication or special privileges
• No user interaction

The vulnerability allows attackers to potentially access configuration files, credential stores, SSL private keys, and other sensitive data stored on the appliance. This information could then be used to conduct further attacks, such as impersonation, credential reuse, or infrastructure mapping.

Detection Methods for CVE-2023-24487

Indicators of Compromise

• Unusual file access patterns in Citrix ADC/Gateway logs, particularly attempts to access system configuration files
• Unexpected HTTP requests with path traversal sequences targeting the appliance
• Evidence of sensitive file reads in audit logs, such as access to /nsconfig/ directories or SSL certificate stores
• Anomalous outbound data transfers from the Citrix appliance

Detection Strategies

• Monitor Citrix ADC and Gateway access logs for suspicious file read attempts or unusual request patterns
• Implement network-based intrusion detection rules to identify exploitation attempts targeting this vulnerability
• Deploy web application firewall rules to detect and block path traversal attempts
• Review authentication logs for any suspicious activity following potential file disclosure

Monitoring Recommendations

• Enable comprehensive logging on all Citrix ADC and Gateway appliances
• Configure SIEM alerts for unusual file access patterns or failed file operations on Citrix appliances
• Implement network traffic analysis to detect potential data exfiltration following successful exploitation
• Establish baseline behavior for Citrix appliance file access to identify anomalies

How to Mitigate CVE-2023-24487

Immediate Actions Required

• Identify all Citrix ADC and Gateway appliances in your environment and their current firmware versions
• Apply the security patches provided by Citrix immediately following the guidance in CTX477714
• If patching is not immediately possible, implement network segmentation to limit exposure of vulnerable appliances
• Review Citrix appliance logs for any signs of prior exploitation attempts
• Rotate any credentials or certificates stored on potentially compromised appliances

Patch Information

Citrix has released security updates to address CVE-2023-24487. Organizations should consult the Citrix Security Bulletin CTX477714 for specific version information and download links for patched firmware. It is critical to update to the latest patched versions for all affected product lines including standard, FIPS, and NDCPP editions.

Workarounds

• Restrict network access to Citrix ADC and Gateway management interfaces to trusted IP addresses only
• Implement web application firewall rules to filter potentially malicious requests before they reach the appliance
• Enable additional logging and monitoring to detect exploitation attempts while working toward patching
• Consider temporarily disabling non-essential services on the appliance to reduce attack surface until patches can be applied

# Example: Restrict management access via Citrix ADC CLI
# Limit management access to specific trusted networks
add ns ip <management_ip> <subnet_mask> -mgmtAccess ENABLED -restrictAccess ENABLED
set ns param -restrictedtimeout 900

# Enable detailed logging for file access monitoring
set audit nslogparams -logLevel ALL