How Attackers Gain Control of Federation Server’s Private Key

The Golden SAML assault is a lesser-known but much more dangerous threat in a world where password-based hacks breach millions of accounts every month.

Unlike common password sprays or phishing attempts, Golden SAML attacks are rare, with Microsoft reporting only 20 incidents across fewer than ten unique customers over the past 24 months as of June 2025.

However, their impact is catastrophic, potentially compromising every account within an organization by exploiting the trust mechanisms of Security Assertion Markup Language (SAML) authentication.

This advanced attack targets the private key of federation servers, like Active Directory Federated Services (AD FS), allowing attackers to forge authentic-looking tokens and impersonate any user within a system, effectively bypassing security controls with stealth and precision.

Mechanics of the Attack

At the heart of a Golden SAML attack lies the abuse of Public Key Cryptography (PKC), the bedrock of SAML’s trust model.

SAML, a 2005 Internet standard, enables single sign-on (SSO) by delegating authentication from relying parties (RPs), such as applications, to identity providers (IdPs) like Microsoft Entra ID or on-premises federation servers.

These servers sign tokens with a private key to prove authenticity, while the corresponding public key is widely distributed for validation.

If attackers gain administrative control of a federation server often through sophisticated breaches they can steal this private key.

With it, they forge SAML tokens that appear legitimate to RPs, granting unrestricted access to resources across cloud and on-premises environments. This is akin to forging an untraceable master key for every door in a kingdom.

Named by CyberArk in 2017, Golden SAML mirrors the Kerberos Golden Ticket attack, but its reach extends further in today’s cloud-centric world, affecting platforms like Azure and AWS.

What makes this attack particularly dangerous is its invisibility; since it doesn’t exploit a vulnerability but rather misuses legitimate mechanisms post-compromise, detection is challenging, and attackers can persist undetected with elevated privileges.

Defending Against the Silent Threat

The most effective defense against Golden SAML attacks is to minimize reliance on on-premises federation servers by migrating to cloud-based identity solutions like Microsoft Entra ID, which eliminates the risk of managing vulnerable signing keys.

For organizations unable to transition immediately, robust security measures are critical.

Using hardware security modules (HSMs) to safeguard private keys, running the latest Windows Server versions (such as Windows Server 2025), and enforcing Zero Trust principles with strict network isolation and just-in-time admin access are essential steps.

Additionally, tools like Microsoft Entra ID Protection and Defender for Identity can detect anomalies indicative of Golden SAML activity, while policies limiting trust delegation and enforcing multi-factor authentication (MFA) via cloud IdPs can mitigate damage.

In hybrid setups, isolating cloud environments from on-premises infrastructure is vital to prevent a breach from cascading.

Though rare, the Golden SAML attack underscores the need for proactive defense, as a single successful exploit can unravel an organization’s entire security fabric, making preparation and vigilance non-negotiable in today’s threat landscape.

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