CVE-2023-41678: Fortinet FortiOS Use After Free Vulnerability

CVE-2023-41678 Overview

CVE-2023-41678 is a double free vulnerability [CWE-415] affecting Fortinet FortiOS and FortiPAM. An authenticated attacker can execute unauthorized code or commands by sending a specifically crafted request to a vulnerable device. The flaw impacts FortiOS versions 7.0.0 through 7.0.5 and multiple FortiPAM 1.0.x and 1.1.x releases.

Fortinet published the issue in advisory FG-IR-23-196. The vulnerability requires low privileges and no user interaction, and it can be exploited over the network. Successful exploitation compromises confidentiality, integrity, and availability of the targeted device.

Critical Impact
Authenticated remote attackers can corrupt memory through a double free and execute arbitrary code on FortiOS and FortiPAM appliances that often sit at network perimeters.

Affected Products

Fortinet FortiOS versions 7.0.0 through 7.0.5
Fortinet FortiPAM versions 1.0.0 through 1.0.3
Fortinet FortiPAM versions 1.1.0 through 1.1.1

Discovery Timeline

2023-12-13 - CVE-2023-41678 published to the National Vulnerability Database (NVD)
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-41678

Vulnerability Analysis

The vulnerability is a double free condition classified under [CWE-415]. A double free occurs when the same memory region is released twice through calls to free() or an equivalent deallocator. The second deallocation corrupts heap metadata, including freelist pointers maintained by the memory allocator.

An attacker who controls subsequent allocations can shape the heap so that the corrupted metadata returns an attacker-chosen pointer on the next allocation. Writes through that pointer then redirect execution flow, typically by overwriting function pointers, virtual table entries, or saved return addresses. The end result on FortiOS is unauthorized command or code execution within the context of the affected process.

Root Cause

The defect resides in request handling logic that releases a heap buffer on more than one error or cleanup path. A specifically crafted request reaches a code path that frees an object and then frees it again before the pointer is cleared. The pointer remains a dangling reference that the allocator treats as reusable memory.

Attack Vector

The attack vector is network based and requires low-level authentication to the management or service interface exposed by FortiOS or FortiPAM. The attacker sends a malformed or sequence-specific request that triggers the duplicated free. No user interaction is required, and the scope remains unchanged within the appliance.

No public proof-of-concept code is available for CVE-2023-41678. The vulnerability mechanism is described in prose because verified exploit artifacts are not published. Consult the FortiGuard Security Advisory FG-IR-23-196 for vendor-supplied technical context.

Detection Methods for CVE-2023-41678

Indicators of Compromise

Unexpected process crashes, watchdog restarts, or kernel panics on FortiOS or FortiPAM devices coinciding with inbound administrative or service requests.
Authentication events from unusual source addresses immediately followed by malformed protocol traffic to management interfaces.
New or modified administrator accounts, configuration changes, or scheduled tasks that do not match approved change records.

Detection Strategies

Inspect FortiOS event logs and crash reports for repeated daemon restarts that align with external request timestamps.
Correlate authenticated session activity with abnormal request patterns targeting REST, SSL VPN, or management endpoints.
Monitor egress traffic from Fortinet appliances for outbound connections to untrusted infrastructure that would indicate post-exploitation command-and-control.

Monitoring Recommendations

Forward FortiOS syslog, crash, and authentication telemetry to a centralized SIEM or data lake for retention and correlation.
Enable alerting on configuration changes, administrator account creation, and firmware integrity events on Fortinet devices.
Track the running firmware version of every appliance against the fixed releases listed in FG-IR-23-196 to detect drift.

How to Mitigate CVE-2023-41678

Immediate Actions Required

Inventory all FortiOS 7.0.x and FortiPAM 1.0.x and 1.1.x devices and identify those running affected versions.
Restrict management and administrative interface access to trusted internal networks and named jump hosts.
Rotate administrative credentials and review audit logs for unauthorized authentication or configuration changes.

Patch Information

Fortinet has published fixed versions and remediation guidance in advisory FortiGuard FG-IR-23-196. Administrators must upgrade FortiOS 7.0.x to a vendor-specified fixed release and update FortiPAM 1.0.x and 1.1.x deployments according to the same advisory. Validate firmware integrity after upgrade and review the configuration for changes introduced before patching.

Workarounds

Limit exposure of FortiOS and FortiPAM management interfaces to a dedicated management VLAN protected by access control lists.
Enforce multi-factor authentication for all administrative accounts to raise the cost of obtaining the low privileges required for exploitation.
Disable unused services and protocols on affected appliances until upgrades to fixed firmware are completed.

bash

# Configuration example - restrict administrative access on FortiOS
config system interface
    edit "port1"
        set allowaccess ping https ssh
        set trust-ip-1 10.0.0.0 255.255.255.0
    next
end