CVE-2022-29055: Fortinet FortiProxy DoS Vulnerability

CVE-2022-29055 Overview

CVE-2022-29055 is an uninitialized pointer access vulnerability affecting Fortinet FortiOS and FortiProxy products. This flaw exists in the SSL VPN daemon (sslvpn) and can be exploited by remote attackers—either authenticated or unauthenticated—to crash the service through a specially crafted HTTP GET request. The vulnerability represents a significant denial of service risk for organizations relying on Fortinet's SSL VPN solutions for secure remote access.

Critical Impact

Remote attackers can crash the SSL VPN daemon without authentication, potentially disrupting secure remote access for all VPN users and impacting business continuity.

Affected Products

• Fortinet FortiOS version 7.2.0
• Fortinet FortiOS versions 7.0.0 through 7.0.5, 6.4.0 through 6.4.8, 6.2.0 through 6.2.10, and 6.0.x
• Fortinet FortiProxy versions 7.0.0 through 7.0.4, 2.0.0 through 2.0.9, 1.2.x, and 7.2.0

Discovery Timeline

• October 18, 2022 - CVE-2022-29055 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-29055

Vulnerability Analysis

This vulnerability is classified as CWE-824 (Access of Uninitialized Pointer). The sslvpn daemon in affected Fortinet products fails to properly initialize a pointer before use during the processing of certain HTTP GET requests. When the daemon attempts to dereference this uninitialized pointer, it accesses arbitrary or invalid memory locations, resulting in a crash of the SSL VPN service.

The attack can be executed remotely over the network without requiring any user interaction or authentication. This makes it particularly dangerous for internet-facing FortiGate and FortiProxy appliances with SSL VPN services enabled. While the vulnerability does not allow for data exfiltration or code execution, the availability impact is significant as it can render remote access infrastructure unavailable.

Root Cause

The root cause is improper memory management within the sslvpn daemon's HTTP request handling code. When processing specific HTTP GET requests, the code path fails to ensure that a pointer variable is properly initialized before being dereferenced. This uninitialized memory may contain garbage data or null values, leading to unpredictable behavior and ultimately a service crash when the pointer is used.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker simply needs network access to the SSL VPN service (typically exposed on port 443 or a custom HTTPS port) to send the malicious HTTP GET request. The attack flow involves:

1. Attacker identifies a Fortinet device with SSL VPN enabled
2. Attacker crafts a specific HTTP GET request targeting the sslvpn daemon
3. The malformed request triggers a code path where an uninitialized pointer is accessed
4. The sslvpn daemon crashes, denying service to legitimate VPN users

The vulnerability can be exploited repeatedly to cause persistent denial of service, preventing users from establishing or maintaining VPN connections. For technical details on the specific attack methodology, refer to the FortiGuard Security Advisory.

Detection Methods for CVE-2022-29055

Indicators of Compromise

• Unexpected crashes or restarts of the sslvpn daemon process on FortiGate or FortiProxy appliances
• Unusual HTTP GET requests in SSL VPN access logs that precede service disruptions
• Multiple VPN user disconnections occurring simultaneously without network issues
• System logs showing daemon crashes with memory access violations or segmentation faults

Detection Strategies

• Monitor FortiGate/FortiProxy system event logs for sslvpn daemon crash events and unexpected restarts
• Implement network-level monitoring to detect anomalous HTTP GET request patterns targeting SSL VPN endpoints
• Configure SNMP traps or syslog alerts for VPN service availability monitoring
• Deploy SentinelOne Singularity to monitor network appliance health and detect exploitation attempts

Monitoring Recommendations

• Enable detailed logging for SSL VPN services on affected Fortinet devices
• Set up automated alerting for sslvpn process crashes or high restart frequencies
• Monitor VPN connection metrics for sudden drops in active sessions that may indicate service disruption
• Implement external availability monitoring for SSL VPN endpoints to detect outages quickly

How to Mitigate CVE-2022-29055

Immediate Actions Required

• Upgrade FortiOS to version 7.2.1 or later, 7.0.6 or later, 6.4.9 or later, or 6.2.11 or later
• Upgrade FortiProxy to version 7.2.1 or later, 7.0.5 or later, or 2.0.10 or later
• Review and restrict network access to SSL VPN services to only necessary IP ranges if upgrades cannot be immediately applied
• Enable rate limiting on SSL VPN endpoints to reduce the impact of potential exploitation attempts

Patch Information

Fortinet has released security patches addressing this vulnerability. Administrators should apply the appropriate firmware updates based on their current version. Refer to the FortiGuard Security Advisory FG-IR-22-086 for specific version information and download links. Organizations should prioritize patching internet-facing devices with SSL VPN services enabled.

Workarounds

• Restrict SSL VPN access to known IP ranges using firewall rules if patching is not immediately feasible
• Implement geographic IP blocking if VPN users are located in specific regions
• Consider temporarily disabling SSL VPN and using alternative remote access methods until patching is complete
• Enable automatic service restart policies to minimize downtime in case of exploitation

# Configuration example: Restrict SSL VPN access to specific IP ranges
config firewall address
    edit "Allowed_VPN_Networks"
        set subnet 10.0.0.0 255.0.0.0
    next
end

config firewall policy
    edit 0
        set srcintf "wan1"
        set dstintf "ssl.root"
        set srcaddr "Allowed_VPN_Networks"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "HTTPS"
    next
end