CVE-2026-13046 in Fireware OS
Summary
by MITRE • 09/30/2026
A deserialization of untrusted data vulnerability in WatchGuard Fireware OS's SAML single sign-on session handling (samld) allows an attacker who has already obtained the ability to write files on the appliance to execute arbitrary code in the context of the samld service by causing samld to load a maliciously crafted session file.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified involves a critical deserialization flaw within the SAML single sign-on implementation, specifically affecting the samld daemon in WatchGuard Fireware OS. This security weakness stems from the application's failure to properly validate and sanitize data before processing it during the session management phase of the authentication workflow. When an attacker gains initial access sufficient to write files on the appliance, they can exploit this lack of input validation by crafting a malicious session file designed to trigger unsafe deserialization operations within the samld service. The core technical flaw lies in the system's trust assumption regarding serialized objects loaded from disk, where no rigorous integrity checks or type constraints are applied before execution. This allows an attacker to inject arbitrary Java object definitions that, when processed by the vulnerable component, result in the instantiation of malicious classes and subsequent command execution with the privileges assigned to the samld service account.
From a technical perspective, this vulnerability is classified under CWE-502, which denotes deserialization of untrusted data. The attack vector requires prior file system access on the target appliance, indicating that this flaw typically follows an initial compromise or privilege escalation event rather than serving as a remote code execution entry point from the network directly. However, its impact significantly amplifies the severity of any preceding vulnerabilities by allowing lateral movement and service-level privilege abuse within the firewall's internal architecture. The samld process handles sensitive authentication tokens and session states; therefore, compromising this daemon grants an attacker control over identity verification mechanisms and potentially allows for persistence or further exploitation of other services that rely on SAML assertions. This aligns with ATT&CK technique T1059, Command and Scripting Interpreter, as the deserialization leads to arbitrary code execution, and also relates to T1078, Valid Accounts, by undermining the integrity of single sign-on sessions.
The operational impact of this vulnerability is severe for organizations relying on WatchGuard firewalls for network perimeter security and identity federation. An attacker who successfully exploits this flaw can achieve remote code execution within the context of the samld service, which often runs with elevated privileges necessary to interact with authentication backends such as Active Directory or other Identity Providers. This capability enables the attacker to exfiltrate sensitive configuration data, manipulate user sessions, bypass access controls, and potentially pivot to internal network segments protected by the firewall. The ability to execute arbitrary code means that standard security boundaries enforced by the device can be circumvented, leading to a complete compromise of the appliance's integrity and availability.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is to apply the vendor-provided software updates or patches that address this specific deserialization flaw in the samld component. Organizations should verify their current firmware version against WatchGuard’s security advisories and prioritize upgrades for appliances exposed to untrusted networks or those with known file system vulnerabilities. Additionally, implementing strict access controls on the appliance's management interface is crucial; ensuring that only authorized administrators have write permissions to critical configuration directories can prevent attackers from placing malicious session files even if other weaknesses are present. Enabling multi-factor authentication for administrative access and regularly auditing file integrity using tools like AIDE or Tripwire can also help detect unauthorized modifications indicative of exploitation attempts. Finally, segmenting management traffic from data plane traffic reduces the attack surface available to potential adversaries seeking initial footholds on the device.