CVE-2024-35279: Fortinet FortiOS Buffer Overflow Flaw

CVE-2024-35279 Overview

A stack-based buffer overflow vulnerability (CWE-121) has been identified in Fortinet FortiOS that could allow a remote unauthenticated attacker to execute arbitrary code or commands. The vulnerability exists in the CAPWAP (Control And Provisioning of Wireless Access Points) control functionality and can be exploited via specially crafted UDP packets. Successful exploitation requires the attacker to evade FortiOS stack protections and depends on the fabric service running on an exposed interface.

Critical Impact

Remote unauthenticated attackers could achieve arbitrary code execution on vulnerable FortiOS devices, potentially compromising network infrastructure security and enabling further attacks on connected systems.

Affected Products

• Fortinet FortiOS version 7.2.4 through 7.2.8
• Fortinet FortiOS version 7.4.0 through 7.4.4
• FortiOS devices with fabric service running on exposed interfaces

Discovery Timeline

• 2025-02-11 - CVE CVE-2024-35279 published to NVD
• 2025-07-17 - Last updated in NVD database

Technical Details for CVE-2024-35279

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-121), which occurs when data is written beyond the boundaries of a fixed-size buffer allocated on the stack. In the context of FortiOS, the vulnerability exists within the CAPWAP control protocol handler, which is responsible for managing wireless access point communications and fabric service operations.

The attack requires network access and involves sending maliciously crafted UDP packets to the target device. While the attack complexity is elevated due to the need to bypass FortiOS stack protection mechanisms, successful exploitation could result in complete compromise of the affected system with full impact to confidentiality, integrity, and availability.

Root Cause

The root cause of CVE-2024-35279 is improper bounds checking in the CAPWAP control packet processing code within FortiOS. When the fabric service processes incoming UDP packets, insufficient validation of packet length or content allows an attacker to overflow a stack-allocated buffer. This classic memory corruption vulnerability can overwrite critical stack data including return addresses and saved registers.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker must be able to send UDP packets to a FortiOS device with the fabric service running on an exposed network interface. The exploitation process involves:

1. Identifying a vulnerable FortiOS device with fabric service enabled on an accessible interface
2. Crafting malicious UDP packets designed to trigger the buffer overflow in the CAPWAP control handler
3. Bypassing FortiOS stack protections (such as stack canaries or ASLR) to achieve reliable code execution
4. Executing arbitrary code or commands with the privileges of the FortiOS process

While stack protections add complexity to exploitation, sophisticated attackers may leverage additional vulnerabilities or information disclosure issues to bypass these mitigations. The vulnerability mechanism involves specially crafted UDP packet payloads that exceed expected buffer sizes in the CAPWAP control processing logic, leading to stack corruption and potential control flow hijacking.

Detection Methods for CVE-2024-35279

Indicators of Compromise

• Unusual or malformed UDP traffic targeting CAPWAP control ports on FortiOS devices
• Unexpected process crashes or restarts in FortiOS fabric service components
• Anomalous network connections originating from FortiOS devices to external systems
• Evidence of unauthorized command execution or configuration changes on FortiOS devices

Detection Strategies

• Deploy network intrusion detection rules to identify malformed or oversized CAPWAP UDP packets
• Monitor FortiOS system logs for crash events, segmentation faults, or service restarts
• Implement network traffic analysis to detect unusual UDP patterns targeting FortiOS management interfaces
• Review FortiOS device configurations to identify systems with fabric service exposed to untrusted networks

Monitoring Recommendations

• Enable enhanced logging on FortiOS devices to capture detailed CAPWAP and fabric service events
• Configure alerting for unexpected service restarts or process crashes on FortiOS infrastructure
• Implement network segmentation monitoring to detect lateral movement from potentially compromised devices
• Regularly audit firewall rules to ensure CAPWAP and fabric service traffic is restricted to trusted sources

How to Mitigate CVE-2024-35279

Immediate Actions Required

• Upgrade FortiOS to a patched version as specified in Fortinet's security advisory
• Restrict network access to fabric service interfaces using firewall rules
• Disable fabric service on interfaces exposed to untrusted networks if not required
• Implement network segmentation to limit exposure of FortiOS management interfaces

Patch Information

Fortinet has released security patches to address this vulnerability. Organizations should consult the Fortinet Security Advisory FG-IR-24-160 for specific remediation guidance and updated firmware versions. Upgrading to a FortiOS version outside the affected ranges (7.2.4 through 7.2.8 and 7.4.0 through 7.4.4) is the recommended remediation approach.

Workarounds

• Configure firewall rules to block UDP traffic to CAPWAP control ports from untrusted sources
• Disable fabric service on externally-facing interfaces if the feature is not operationally required
• Implement strict network access controls limiting which systems can communicate with FortiOS management interfaces
• Enable and configure FortiOS intrusion prevention features to detect and block exploit attempts

For environments where immediate patching is not feasible, restricting network access to the fabric service interface provides significant risk reduction. Ensure that only trusted management networks can reach the vulnerable service by implementing ACLs or firewall rules at the network boundary.