CVE-2021-22908: Ivanti Connect Secure RCE Vulnerability

CVE-2021-22908 Overview

A buffer overflow vulnerability exists in the Windows File Resource Profiles functionality of Ivanti Connect Secure (formerly Pulse Connect Secure) version 9.X. This vulnerability allows a remote authenticated user with privileges to browse SMB shares to execute arbitrary code as the root user on affected systems. As of version 9.1R3, the vulnerable permission is not enabled by default, reducing the attack surface for newer deployments.

Critical Impact

Remote authenticated attackers can achieve root-level code execution on vulnerable Ivanti/Pulse Connect Secure appliances, potentially compromising the entire VPN infrastructure and gaining unauthorized access to internal networks.

Affected Products

• Ivanti Connect Secure 9.0 (all releases through 9.0r6.0)
• Ivanti Connect Secure 9.1 (all releases through 9.1r11.4)
• Pulse Secure Pulse Connect Secure 9.0rx

Discovery Timeline

• May 27, 2021 - CVE-2021-22908 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-22908

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw resides in the Windows File Resource Profiles component, which handles SMB share browsing functionality within the VPN appliance. When processing certain inputs related to file resource operations, the application fails to properly validate the size of user-supplied data before copying it into a fixed-size memory buffer.

The vulnerability requires authentication, meaning an attacker must first have valid credentials to access the VPN appliance. However, once authenticated, an attacker with permissions to browse SMB shares can craft malicious requests that overflow the vulnerable buffer. This memory corruption can be leveraged to overwrite critical data structures, ultimately allowing arbitrary code execution with root privileges.

Root Cause

The root cause is improper bounds checking in the code responsible for handling Windows File Resource Profiles operations. When processing SMB share browsing requests, the application copies user-controlled data into a stack or heap buffer without verifying that the input length does not exceed the allocated buffer size. This classic buffer overflow condition (CWE-120) allows attackers to corrupt adjacent memory and potentially hijack program execution flow.

Attack Vector

The attack is network-based and requires the attacker to have authenticated access to the Ivanti/Pulse Connect Secure appliance. The specific attack path involves:

1. Authenticating to the VPN appliance with valid user credentials
2. Having or obtaining permissions to browse SMB shares (note: disabled by default in 9.1R3+)
3. Sending specially crafted requests through the Windows File Resource Profiles functionality
4. Triggering the buffer overflow condition to corrupt memory
5. Achieving arbitrary code execution with root privileges

The vulnerability mechanism exploits insufficient input validation in the SMB share browsing functionality. When a user with appropriate permissions interacts with Windows File Resources, the application processes the request through a code path that fails to properly bounds-check input data. An attacker can supply an oversized input value that exceeds the allocated buffer, overwriting adjacent memory regions. This memory corruption can be weaponized to redirect program execution to attacker-controlled code, resulting in root-level compromise of the appliance. For complete technical details, refer to the CERT Vulnerability Note #667933 and the Pulse Secure Security Advisory SA44800.

Detection Methods for CVE-2021-22908

Indicators of Compromise

• Unexpected process crashes or restarts of the Pulse/Ivanti Connect Secure appliance services
• Anomalous memory usage patterns or segmentation faults in system logs
• Unusual root-level processes spawned from the web application context
• Suspicious SMB share browsing activity from unexpected user accounts
• Evidence of lateral movement originating from the VPN appliance

Detection Strategies

• Monitor VPN appliance logs for errors related to Windows File Resource Profiles or SMB functionality
• Implement network traffic analysis to detect unusual patterns in authenticated sessions
• Deploy integrity monitoring on critical VPN appliance files and configurations
• Configure alerting for any unexpected privilege escalation or root process creation
• Review authentication logs for suspicious access patterns to SMB browsing features

Monitoring Recommendations

• Enable verbose logging for Windows File Resource Profiles functionality
• Implement SIEM correlation rules for buffer overflow indicators (crash patterns, memory errors)
• Monitor for unauthorized changes to VPN appliance configurations
• Track user accounts with SMB share browsing permissions and audit their activity
• Deploy endpoint detection on systems that connect through affected VPN appliances

How to Mitigate CVE-2021-22908

Immediate Actions Required

• Apply the latest security patches from Ivanti/Pulse Secure immediately
• Audit all user accounts and remove unnecessary SMB share browsing permissions
• Disable Windows File Resource Profiles functionality if not business-critical
• Implement network segmentation to limit exposure of VPN appliances
• Review VPN appliance logs for evidence of prior exploitation attempts

Patch Information

Ivanti/Pulse Secure has released security updates addressing this vulnerability. Organizations should consult the Pulse Secure Security Advisory SA44800 for specific patch versions and upgrade instructions. Ensure all Ivanti Connect Secure and Pulse Connect Secure appliances are updated to the latest available version that addresses CVE-2021-22908.

Workarounds

• Disable Windows File Resource Profiles functionality entirely if not required for business operations
• Remove SMB share browsing permissions from all users except those with explicit business need
• Implement additional network access controls to limit who can reach the VPN appliance management interfaces
• Deploy a Web Application Firewall (WAF) in front of the VPN appliance to filter potentially malicious requests
• Upgrade to version 9.1R3 or later where the vulnerable permission is disabled by default

For environments where immediate patching is not possible, restricting access to the SMB share browsing functionality significantly reduces the attack surface. Administrators should audit user permissions and disable the Windows File Resource Profiles feature until patches can be applied.