CVE-2024-21894: Ivanti Connect Secure DoS Vulnerability

CVE-2024-21894 Overview

A heap overflow vulnerability has been identified in the IPSec component of Ivanti Connect Secure (versions 9.x and 22.x) and Ivanti Policy Secure. This vulnerability allows an unauthenticated malicious user to send specially crafted requests to crash the service, resulting in a Denial of Service (DoS) attack. Under certain conditions, successful exploitation may also lead to arbitrary code execution, making this a particularly dangerous flaw for organizations relying on these VPN and network access control solutions.

Critical Impact

Unauthenticated attackers can remotely crash Ivanti Connect Secure and Policy Secure services, potentially achieving remote code execution without any user interaction or privileges required.

Affected Products

• Ivanti Connect Secure versions 9.1 (R1 through R18) and 22.1 through 22.6
• Ivanti Policy Secure versions 9.0 (base through R4), 9.1 (base through R18), and 22.1 through 22.6
• All deployments with IPSec functionality enabled

Discovery Timeline

• April 4, 2024 - CVE-2024-21894 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-21894

Vulnerability Analysis

This heap overflow vulnerability (CWE-787: Out-of-bounds Write) exists within the IPSec component of Ivanti's secure access solutions. The flaw stems from improper handling of specially crafted network requests, which can cause the application to write data beyond the boundaries of allocated heap memory. When exploited, this memory corruption can crash the IPSec service immediately, denying legitimate users access to VPN connectivity.

The vulnerability is particularly concerning because it requires no authentication to exploit. An attacker with network access to the vulnerable service can trigger the condition remotely without any user interaction. The IPSec component processes incoming network packets, and malformed input can overflow heap buffers, corrupting adjacent memory structures.

Additionally, the vulnerability is associated with CWE-703 (Improper Check or Handling of Exceptional Conditions), indicating that the affected code lacks adequate error handling when processing malformed input, allowing the overflow condition to proceed unchecked.

Root Cause

The root cause of CVE-2024-21894 lies in insufficient bounds checking within the IPSec packet processing routines. When the IPSec component receives network packets, it allocates heap memory to store and process the data. The vulnerability occurs because the code fails to properly validate the size or format of incoming data before copying it into fixed-size heap buffers. This lack of input validation allows an attacker to provide oversized or malformed data that exceeds the allocated buffer boundaries, resulting in heap corruption.

Attack Vector

The attack vector for this vulnerability is network-based, requiring the attacker to have network connectivity to the vulnerable Ivanti appliance's IPSec service. The attack flow typically follows this pattern:

1. The attacker identifies an exposed Ivanti Connect Secure or Policy Secure gateway with IPSec enabled
2. Specially crafted IPSec packets are sent to the target service
3. The malformed packets trigger the heap overflow condition during processing
4. The service crashes (DoS) or, in certain conditions, attacker-controlled code may execute

The vulnerability can be triggered without authentication, meaning any network-reachable attacker can attempt exploitation. The lack of required privileges or user interaction significantly increases the exploitability of this flaw.

Detection Methods for CVE-2024-21894

Indicators of Compromise

• Unexpected crashes or restarts of IPSec-related services on Ivanti appliances
• Anomalous IPSec traffic patterns including malformed packet structures
• Unusual memory consumption spikes on Ivanti Connect Secure or Policy Secure gateways
• Service availability interruptions correlating with inbound network activity

Detection Strategies

• Deploy network intrusion detection systems (IDS/IPS) with signatures for malformed IPSec packets targeting Ivanti appliances
• Monitor Ivanti appliance logs for service crashes, segmentation faults, or heap corruption errors
• Implement SentinelOne Singularity to detect exploitation attempts through behavioral analysis and memory protection
• Enable verbose logging on IPSec components to capture packet processing anomalies

Monitoring Recommendations

• Establish baseline network traffic patterns to Ivanti gateways and alert on deviations
• Configure automated alerting for IPSec service availability and restart events
• Monitor system health metrics including memory utilization and process stability on affected appliances
• Implement external service monitoring to detect DoS conditions affecting VPN availability

How to Mitigate CVE-2024-21894

Immediate Actions Required

• Verify your Ivanti Connect Secure and Policy Secure version against the affected product list immediately
• Apply the security patches provided by Ivanti as the highest priority remediation action
• If patching is not immediately possible, consider restricting network access to IPSec services
• Review network logs for any suspicious activity that may indicate attempted exploitation

Patch Information

Ivanti has released security patches to address CVE-2024-21894 along with related vulnerabilities (CVE-2024-22052, CVE-2024-22053, and CVE-2024-22023). Organizations should consult the Ivanti Security Advisory for specific patch versions and installation instructions. Given the critical nature of this vulnerability and its network-accessible attack surface, patching should be prioritized immediately.

Workarounds

• Implement network segmentation to limit exposure of Ivanti appliances to trusted networks only
• Deploy firewall rules to restrict IPSec traffic sources to known, authorized IP ranges
• Enable additional network-level monitoring and rate limiting on IPSec services
• Consider temporarily disabling IPSec functionality if not critical to operations until patches can be applied

# Example firewall rule to restrict IPSec access (adapt to your environment)
# Allow IPSec only from trusted corporate networks
iptables -A INPUT -p udp --dport 500 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 4500 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 500 -j DROP
iptables -A INPUT -p udp --dport 4500 -j DROP