Fortinet FortiOS and FortiProxy SSL-VPN contain a heap-based buffer overflow vulnerability which can allow an unauthenticated, remote attacker to execute code or commands via specifically crafted requests.
FREQUENTLY ASKED
What is CVE-2023-27997 and why is it significant for network security?
CVE-2023-27997 is a critical heap-based buffer overflow vulnerability in Fortinet's SSL-VPN component. With a CVSS score of 9.2, it matters because it allows unauthenticated, remote attackers to execute arbitrary code. This bypasses traditional authentication barriers, placing the entire network infrastructure at risk of total compromise and ransomware deployment, especially as it is known to be actively exploited.
Which versions of Fortinet FortiOS and FortiProxy are affected by this vulnerability?
The vulnerability affects several version branches including FortiOS versions 7.2.4, 7.0.11, 6.4.12, 6.2.13, and 6.0.16 and below. For FortiProxy, affected versions include 7.2.3, 7.0.9, 2.0.12 and below, as well as all versions of the 1.2 and 1.1 branches. Organizations should immediately audit their firmware versions against the vendor's PSIRT advisory to determine their specific exposure levels.
Has a patch been released for CVE-2023-27997?
Yes, Fortinet has released official patches to address this heap-based buffer overflow. Remediation requires upgrading to FortiOS 7.4.0, 7.2.5, 7.0.12, 6.4.13, 6.2.14, or 6.0.17 and higher. For FortiProxy users, updates to versions 7.2.4, 7.0.10, or 2.0.13 are necessary. Administrators should prioritize these updates immediately due to the active exploitation status and critical nature of the flaw.
What is the remediation deadline and how does it impact compliance?
The remediation deadline is July 4, 2023. For federal agencies and organizations following CISA's Binding Operational Directive (BOD) 22-01, this date is a mandatory cutoff for applying patches. Failing to meet this deadline can result in non-compliance with federal cybersecurity standards and leaves the organization vulnerable to known exploitation tactics used by ransomware groups and advanced persistent threats.
How can I check if my Fortinet deployment is affected by CVE-2023-27997?
To check if an instance is affected, administrators should log into the FortiOS or FortiProxy management console and verify the current firmware version. If the version matches any of the affected ranges—such as FortiOS 7.2.4 or below—the system is vulnerable. Additionally, administrators should review SSL-VPN logs for unusual requests and check the FortiGuard PSIRT portal for the most current advisory details.
CVE-2023-27997 is a critical heap-based buffer overflow vulnerability (CWE-122) affecting Fortinet FortiOS and FortiProxy SSL-VPN services. With a CVSS score of 9.2 and a CRITICAL severity rating, this flaw allows unauthenticated remote code execution, necessitating immediate patching before the July 04, 2023 remediation deadline.
CVE-2023-27997 centers on a CWE-122: Heap-based Buffer Overflow within the SSL-VPN process of FortiOS and FortiProxy. In technical terms, the heap is a region of a computer's memory used for dynamic memory allocation, where blocks of memory are allocated and freed in an arbitrary order. When a program writes more data to a buffer located on the heap than that buffer can actually hold, it overflows into adjacent memory.
In the context of Fortinet's SSL-VPN, this vulnerability is triggered by specifically crafted HTTPS requests. Because the SSL-VPN must parse complex incoming data before a user is even authenticated, the overflow occurs in a pre-authentication state. An attacker does not need a username or password to exploit this. By carefully structuring the payload, an attacker can overwrite critical control structures in memory, such as function pointers or return addresses, redirecting the execution flow to run arbitrary commands with the privileges of the SSL-VPN process (often root or administrative).
Understanding the SSL-VPN Attack Vector
The attack vector is categorized as NETWORK with LOW complexity. This means any device with the SSL-VPN interface exposed to the public internet is a potential target. Unlike vulnerabilities that require a user to click a link (User Interaction: Required) or a local attacker to have a shell (Attack Vector: Local), CVE-2023-27997 can be exploited at scale via automated scripts scanning the internet for vulnerable FortiOS signatures.
Blast Radius and Threat Landscape
The blast radius for this vulnerability is total (SSVC Technical Impact: Total). Successful exploitation grants the attacker full control over the gateway device. From this vantage point, an adversary can intercept decrypted VPN traffic, steal credentials, pivot into the internal corporate network, or deploy ransomware. The EPSS score of 0.90319 places this vulnerability in the top 0.4% of all known flaws for likelihood of exploitation, a metric supported by the fact that it is already listed in CISA’s Known Exploited Vulnerabilities (KEV) catalog and has been associated with ransomware operations.
Who Is Affected: Impacted Versions and Compliance Requirements
This vulnerability impacts a wide array of legacy and modern Fortinet firmware. If your organization utilizes the SSL-VPN feature on any of the following products, you are at risk:
FortiOS: Versions 7.2.0 through 7.2.4, 7.0.0 through 7.0.11, 6.4.0 through 6.4.12, 6.2.0 through 6.2.13, and 6.0.0 through 6.0.16.
FortiProxy: Versions 7.2.0 through 7.2.3, 7.0.0 through 7.0.9, 2.0.0 through 2.0.12, and all versions of 1.2 and 1.1.
For organizations operating within the United States federal government or those that adhere to the Cybersecurity and Infrastructure Security Agency (CISA) guidelines, Binding Operational Directive (BOD) 22-01 applies. The remediation deadline of July 4, 2023, is a critical compliance milestone. Failure to patch by this date indicates a significant lapse in risk management and increases the likelihood of a successful breach during high-risk periods.
Official Remediation Steps: How to Patch
Fortinet has released updated firmware to mitigate CVE-2023-27997. Security administrators should follow these steps immediately:
Identify Vulnerable Assets: Audit all FortiGate and FortiProxy devices to determine their current firmware version and whether the SSL-VPN service is enabled.
Download Official Patches: Access the Fortinet Support Portal and download the appropriate firmware update based on the following mapping:
Upgrade FortiOS 7.2.x to 7.2.5 or higher.
Upgrade FortiOS 7.0.x to 7.0.12 or higher.
Upgrade FortiOS 6.4.x to 6.4.13 or higher.
Upgrade FortiOS 6.2.x to 6.2.14 or higher.
Upgrade FortiOS 6.0.x to 6.0.17 or higher.
Upgrade FortiProxy 7.2.x to 7.2.4 or higher.
Upgrade FortiProxy 7.0.x to 7.0.10 or higher.
Upgrade FortiProxy 2.x to 2.0.13 or higher.
Validate the Update: After the reboot, verify the firmware version in the CLI using get system status and ensure the SSL-VPN is functioning correctly.
Security Best Practices for Hardening Fortinet Environments
While patching is the primary defense, the following strategies address the underlying CWE-122 risks and provide defense-in-depth:
Disable Unused Services: If SSL-VPN is not required for your business operations, disable the service entirely to eliminate the attack surface.
Implement Geographic Blocking: Use FortiGuard GeoIP filters to restrict access to the SSL-VPN portal to only those countries where your employees are located, reducing exposure to global scanning bots.
Enable Multi-Factor Authentication (MFA): While MFA does not prevent the buffer overflow itself (which occurs pre-auth), it prevents attackers from using credentials they may have scraped from memory post-exploitation.
Monitor for Anomalous Crashes: Repeated crashes of the sslvpnd process can be an indicator of failed or successful exploitation attempts. Configure automated alerts for process restarts.
Transition to Zero Trust Network Access (ZTNA): Move away from traditional SSL-VPNs toward ZTNA, which provides more granular access control and significantly reduces the exposure of the network gateway to unauthenticated traffic.
Egress Filtering: Restrict the outbound traffic allowed from the FortiGate device itself. If an attacker gains code execution, egress filtering can prevent the device from reaching out to a Command and Control (C2) server to download further malware.