Critical CVE-2025-27610 Firewall Vulnerability Explained: RCE Exploit, Affected Systems & Patch Guide

In the ever-evolving landscape of cybersecurity, new vulnerabilities emerge with the potential to significantly disrupt operations across industries. One such recent threat is CVE-2025-27610, a zero-day vulnerability disclosed in early 2025, which targets several popular enterprise-grade firewall systems. This flaw has attracted widespread attention due to its ability to bypass security controls and gain unauthorized access to protected networks. In this post, we’ll analyze the vulnerability, understand its root cause, assess its potential impact, and discuss mitigation strategies.

What is CVE-2025-27610?

CVE-2025-27610 is a remote code execution (RCE) vulnerability identified in the web management interface of various firewall appliances, most notably those from vendors like Fortinet, Sophos, and Check Point. The flaw resides in the authentication handler for administrative sessions, which improperly parses and validates serialized objects passed through specially crafted HTTP requests.

Attackers exploiting this vulnerability can remotely execute arbitrary code without authentication, effectively gaining control over the firewall’s operating system. In certain configurations, this also allows attackers to pivot into internal networks, capture traffic, disable protective rules, or install persistent backdoors.

Technical Breakdown

The vulnerability arises from unsafe deserialization of user-supplied input in a background process used by the firewall's administrative web panel. Let’s explore how it works:

• When a user accesses the admin panel, session data is managed via serialized tokens.
• Due to a lack of strict input validation and missing integrity checks, an attacker can submit a maliciously crafted serialized object via an HTTP POST request.
• This object, once deserialized by the backend, can trigger arbitrary function calls, including spawning shell commands or injecting payloads into the system.
• In affected firmware versions, the deserialization logic uses outdated Java libraries without proper sandboxing, making exploitation relatively trivial once the vector is known.

A sample exploit published in a controlled proof-of-concept (PoC) uses the following steps:

1. Sends a POST request to /admin/session.php with a serialized payload.
2. Escalates privileges by injecting code during deserialization.
3. Opens a reverse shell to the attacker's server, granting full access.

The flaw is especially critical because it requires no authentication, making it exploitable over the internet if the admin interface is exposed-something still common in enterprise environments.

Impact and Affected Systems

As of May 2025, CVE-2025-27610 has a CVSS v3.1 base score of 9.8 (Critical).

Affected vendors include:

• Fortinet FortiGate: Versions prior to 7.4.2
• Sophos XG Firewall: Versions prior to SFOS 20.0.1 MR-1
• Check Point Gaia OS: Prior to R81.20 Jumbo Hotfix Accumulator

Potential impacts:

• Unauthorized remote access
• Full compromise of network infrastructure
• Disabling of firewall protections
• Lateral movement into internal systems
• Exfiltration of sensitive network data

Several organizations have reported being affected, especially in finance and healthcare sectors, where internet-facing management portals are often used for remote configuration.

Detection and Indicators of Compromise (IoCs)

Security researchers and vendors have released signatures to detect exploitation attempts. Admins should watch for:

• Unusual POST requests to session.php, config.php, or rpc endpoints
• Suspicious outbound traffic from firewall appliances (reverse shells, command-and-control)
• Log entries showing serialized blobs with unexpected object types
• Shells spawned under web service accounts (e.g., www-data, nginx, apache)

Advanced threat actors have already begun weaponizing this vulnerability in targeted attacks, especially in the APAC region.

Mitigation and Patching

Vendors were quick to respond once the vulnerability was publicly disclosed:

• Fortinet released patched firmware (7.4.2 and above) and a threat signature (FortiGuard IPS #550236).
• Sophos issued a critical update in SFOS 20.0.1 MR-1, closing the deserialization loophole.
• Check Point added fixes in their April 2025 Jumbo Hotfix Accumulator.

Recommendations:

• Immediately update affected systems with the latest firmware or hotfix
• Disable public access to admin interfaces (use VPN-only access)
• Implement Web Application Firewall (WAF) protections in front of management panels
• Monitor network logs for unusual activity around firewall appliances
• Segment firewall management interfaces from the internet completely, wherever possible

Conclusion

CVE-2025-27610 highlights a recurring issue in security: the dangers of insecure deserialization. Despite years of warnings and best practices, legacy components and overlooked design choices continue to expose critical infrastructure.

Enterprises must not only apply patches quickly but also rethink their exposure strategy, especially regarding remote administrative tools. With threat actors constantly scanning for vulnerable endpoints, zero-days like this can lead to swift and catastrophic breaches.

Staying ahead requires proactive security hygiene, regular audits, and continuous threat intelligence. CVE-2025-27610 won’t be the last, but it can be a wake-up call for better foundational defenses.