Why Never-Expiring SSH Keys Are a Security Risk?

Secure Shell (SSH) is one of the most trusted protocols for remote administration, automation, and secure communication over untrusted networks. It is designed to protect sensitive operations by encrypting network traffic and eliminating the need to send plaintext passwords.

At the heart of SSH authentication lies a key-pair mechanism that allows users and machines to access systems securely without relying on traditional password-based logins.

This is where SSH keys come in. An SSH key pair consists of a private key stored on the client machine and a public key stored on the server. Together, they form a secure handshake that authenticates a user or system without ever exposing secret credentials over the network. Because of their strong security advantages, SSH keys are one of the most widely used mechanisms for secure authentication across servers, applications, and automation workflows.

But unlike passwords or digital certificates, SSH keys don’t naturally expire. Once created, a key pair can remain valid indefinitely, often long after the user’s role has changed, they have left the organization, or the system has been decommissioned. This fundamental characteristic creates one of the most persistent and dangerous blind spots in enterprise security.

Forgotten or orphaned keys can continue to grant access without visibility, making it difficult for organizations to enforce least-privilege policies or maintain proper audit control. Studies repeatedly show that many organizations cannot track all active SSH keys, leaving their infrastructure exposed to misuse, insider threats, and potential breaches.

In this blog, we will take a deeper look at why non-expiring SSH keys create hidden security risks and how organizations can effectively prevent them.

Understanding SSH Keys

SSH keys are cryptographic credentials used by the SSH protocol to authenticate clients and establish secure sessions. Each SSH key pair consists of a public and private key.

A simple way to understand SSH keys is to think of them like a padlock and a key.

The public key is the padlock. It’s not sensitive, and you can make as many copies as you want. You place this padlock on any remote machine you want to access by adding it to the authorized_keys file in the ~/.ssh folder. Once the padlock is in place, that machine knows it should trust anyone who can open it.

The private key, on the other hand, is the actual key that unlocks that padlock. This key stays with you and must be kept secret and protected, just like a real key. When you try to connect to a remote system, SSH checks whether your private key can unlock the padlock (public key) stored on the server. If it can, access is granted securely and without needing a password.

Now that we understand what SSH keys are, let us look at how they work in practice to better understand the risks they can introduce.

How SSH Keys Work?

As you now know, SSH key-based authentication relies on a cryptographic key pair that is almost always generated on the client system. Traditionally, the private key remains securely stored on the client machine, while the corresponding public key is copied to the server and saved inside the ~/.ssh/authorized_keys file.

When the client attempts to initiate a connection, the SSH server checks the incoming request and looks for a matching public key in the authorized keys file. If a match is found, the server sends a cryptographic challenge to the client. The client signs this challenge using its private key without ever transmitting the key itself and sends the signed response back to the server. The server then verifies the signature using the stored public key.

If verification succeeds, the client is authenticated without ever transmitting the private key or any password over the network. All of this happens automatically and securely, without any manual action from the user, and no passwords are transmitted over the network.

In practice, SSH key authentication works like using a username and password to log in, but in a far more secure and convenient way. Once your public key is registered on a remote system, you can connect from your local machine without typing credentials and use your terminal as if you were sitting at the remote computer itself. That means you can run commands such as ls, cd, or any administrative actions, all through an encrypted channel.

It is often misunderstood that this encrypted channel is protected by your private key. In reality, SSH uses your asymmetric key pair only during the authentication to verify identity and negotiate the session key. Once the connection is verified, SSH switches to a faster symmetric session key, and all commands, files, and terminal data are encrypted using this symmetric key for the rest of the session.

Since the private key never leaves the client device and is resistant to brute force attacks, SSH key authentication is considered one of the most secure authentication mechanisms available for remote access. However, this strength comes with one significant limitation that often goes overlooked. We will explore that limitation in the next section.

Why SSH Keys Don’t Expire and Why That’s a Problem?

While SSH key authentication is secure and convenient, it comes with a hidden risk. By default, SSH keys do not expire on their own. Once a public key is added to the authorized_keys file on a server, it remains valid indefinitely, unless manually removed. While this simplifies administration, it creates long-term security risks. Keys that are no longer needed, or that belong to former employees or retired systems, can continue to grant access and often go unnoticed.

SSH was designed to provide strong encryption and reliable authentication, but it does not include built-in mechanisms for key expiration, renewal, or automated validity checks. As a result, organizations often experience SSH key sprawl, the uncontrolled accumulation of keys across servers, accounts, and environments. In essence, key sprawl occurs when old, unused, or orphaned keys pile up over time, creating hidden access points that are difficult to track.

A study highlighted that 57% of respondents considered managing SSH keys to be painful and difficult. It stated that by 2024, increased awareness and better practices reduced this number to 27%, yet key management remains a significant challenge in many organizations. This demonstrates that while the issue is better understood, the risks of unmanaged keys persist.

The consequences of unmanaged SSH keys include:

• Persistent Access

  Keys remain valid even after employees leave the organization or their roles change. This allows former users to retain access to critical systems, creating a significant insider threat vector or a point of compromise if their personal machine is ever breached. This severely violates the principle of least privilege.

• Stale Keys

  Disabled or inactive accounts may still have active keys on servers, leaving hidden access points that could be exploited by attackers.

• Key Duplication

  When servers are cloned, migrated, or backed up, embedded SSH keys often get copied along with them. This creates multiple copies of the same key across systems, unintentionally extending access and increasing exposure.

• Loss of Accountability

  Over time, it becomes unclear who created a key, who owns it, or whether it’s still required. Without a proper inventory, correlating or mapping keys to their respective owners, systems, or applications becomes nearly impossible, making incident response, audits, and access reviews extremely difficult.

• No Automatic Cleanup

  Keys created five or ten years ago continue to authenticate without interruption. When there is no defined schedule for rotation or revocation, these dormant keys significantly increase the risk of compromise, privilege creep, and unauthorized access.

• Hidden Attack Surface

  The combined effect of persistent, stale, duplicate, and unmonitored keys results in a large, hidden attack surface across the organization. Adversaries can exploit these orphaned or forgotten keys to move laterally and escalate privileges.

Without proper key lifecycle management, these unmanaged keys can lead to serious security, operational, and compliance challenges. In the next section, we’ll explore these risks in detail to understand why addressing them is critical for your organization.

Security, Operational, and Compliance Risks

Long-lived SSH keys introduce multiple risks that grow silently over time. Some of the major risks include:

1. Unbounded Access

   A non-expiring key essentially becomes a permanent backdoor. If the private key is ever exposed through endpoint compromise, Git repos, backups, or old employee devices, attackers gain unrestricted access to critical servers and systems.

2. Privilege Creep

   Keys mapped to privileged accounts (root, admin, service accounts) accumulate over the years, giving far more access than necessary. Employees change roles, projects end, and services are deprecated, yet old keys often remain active. This violates least-privilege principles and often goes undetected.

3. Management Overhead

   Manually tracking, distributing, rotating, and revoking keys across hundreds or thousands of systems is time-consuming and prone to errors. Onboarding new employees becomes difficult, as ensuring timely and appropriate access is challenging without centralized key management, while offboarding poses a risk of forgotten keys leaving open access points.

4. Zero Visibility During Incidents

   In the event of a security incident, responders face significant challenges. Without key usage timestamps, expiration dates, or centralized logging, it is difficult to determine which keys are active, who is using them, or which systems have been accessed. This hampers forensic analysis and prolongs remediation efforts.

5. Compliance Failures

   Frameworks such as NIST 800-53, CIS Controls, ISO 27001, and SOX require credential rotation, access reviews, and proper identity binding. Non-expiring SSH keys directly conflict with these requirements, leaving organizations exposed to compliance gaps and regulatory penalties.

6. Unmanaged Automation Risks

   Automation workflows such as CI/CD pipelines, cron jobs, and integration scripts often rely on SSH keys. These keys rarely get audited, rotated, or removed, making them ideal targets for attackers moving laterally inside the network. With many organizations still lacking centralized key management and relying on manual processes like spreadsheets, the risk of overlooked or orphaned keys in automated workflows is alarmingly high, leaving critical systems exposed to compromise.

Now that we have gone through the risks, let us take a look at how organizations can tackle these risks with proper SSH key lifecycle management.

Mitigating Risks of Never-Expiring SSH Keys

Many organizations struggle not because SSH is weak, but because the way SSH is deployed, monitored, and governed leaves room for attackers to blend in as legitimate users. To address this risk, organizations need a structured approach for managing SSH keys throughout their lifecycle to reduce exposure, enforce accountability, and maintain control. A strong SSH key lifecycle management strategy includes:

1. Centralized Key Management

   Centralizing SSH key management ensures consistent control, reduces operational complexity, and prevents key sprawl. A centralized SSH key management platform/strategy provides:

   • Visibility: Complete inventory of all keys, including owner, purpose, and usage history.
   • Policy Enforcement: Standardized rotation intervals, approved key types, and minimum key lengths.
   • Automated Provisioning & Deprovisioning: Controlled issuance and immediate removal when access is no longer required.
   • Auditing & Reporting: Compliance verification, forensic readiness, and governance oversight.
   Centralization transforms SSH keys from unmanaged artifacts into accountable and auditable credentials.

2. Key Rotation

   Regular rotation ensures that SSH keys remain short-lived, regenerated periodically, and invalidated before becoming stale. Frequent rotation reduces the impact of key theft and enforces visibility into which keys exist and why.

   Recommended best practices:

   • Rotate user keys every 90 days or align with corporate password policies.
   • Rotate service or automation account keys every 180 days or based on risk level.
   • Automate rotation through centralized tools rather than relying on manual updates.

3. Key Revocation

   Keys associated with users who leave the organization, retired systems, or suspected compromises must be revoked immediately.

   Revocation involves:

   • Removing public keys from all authorized_keys files.
   • Updating centralized repositories and inventories.
   • Logging and confirming removal for audit purposes.
   This prevents forgotten or orphaned keys from persisting in production environments.

4. Adopt Ephemeral SSH Keys (Short-Lived Access)

   Instead of static keys, modern environments are moving to ephemeral SSH keys generated on demand and valid only for a short duration, often minutes or hours.

   Benefits include:

   • Eliminates long-term exposure of static keys.
   • Automatically expires when the session or time window ends.
   • Integrates with identity providers and just-in-time access workflows, enabling authentication that naturally expires as soon as the session or window closes.

5. Move Toward Short-Lived Certificates (SSH CA)

   Organizations with mature security programs are adopting SSH Certificate Authorities to replace static keys with short-lived SSH certificates.

   Benefits include:

   • Built-in expiration.
   • Strong identity binding for each user or system.
   • Centralized trust model eliminating the need to distribute public keys manually.
   • Completely resolves the “never-expire” problem while supporting automated key management workflows.

6. Operational Hardening of SSH Access

   While managing SSH keys is critical, it is equally important to harden SSH configurations on servers. Misconfigured SSH services can expose critical systems even if key management is strong. Key operational hardening measures include:

   • Disable root login:

     One of the first steps is to disable direct root login, as allowing root access bypasses auditing and accountability, giving attackers full control over the system if credentials or keys are compromised. Instead, individual user accounts with administrative privileges should be used via sudo, which ensures that all actions are traceable and authorized.

   • Change the default SSH port:

     Another key measure is to change the default SSH port from 22/TCP. Default ports are well-known and frequently targeted by automated brute-force attacks or port scanners; moving SSH to a non-standard port reduces exposure, although it should complement, not replace, other security measures.

   • Restrict logins by IP:

     Limit SSH access only to known and trusted networks. Leaving SSH open to the public internet gives attackers endless chances to probe the server, brute-force credentials, or exploit weaknesses, so restricting access to specific IPs significantly reduces exposure.

   • Disable X11/TCP forwarding when not needed:

     SSH features like X11 and TCP forwarding are useful for graphical applications or tunneling traffic, but can be exploited to access client systems or redirect sensitive data. Disabling these features unless explicitly required and restricting them to trusted users minimizes this risk.

   • Block accounts with blank passwords:

     Accounts with blank passwords provide trivial access points, bypassing other security controls, so all such accounts must be blocked, and strong authentication should be enforced.

   • Enforce public key authentication:

     To strengthen authentication, public key-based login should be mandated, replacing passwords with cryptographic keys. Public key authentication is more secure, resists brute-force attacks, supports automated workflows, and enables password-less login while maintaining strong encryption.

7. Policy and Monitoring

   A formal SSH key management policy ensures consistent governance. It recommends:

   • Maintaining an up-to-date inventory of all SSH keys and regularly validating their ownership, purpose, and usage.
   • Immediate revocation and replacement of keys that are compromised or suspected to be compromised.
   • Monitoring for leaked or exposed public keys, which may disclose details about private infrastructure.
   • Regular audits and access reviews to detect and remove orphaned, stale, duplicate, or unauthorized keys.

Implementing these strategies ensures that SSH keys remain tightly controlled, auditable, and secure throughout their lifecycle, mitigating operational, security, and compliance risks. However, executing these strategies effectively can be complex, and this is where Encryption Consulting comes in.

How Can Encryption Consulting Help?

At Encryption Consulting, we understand the challenges enterprises face in managing SSH keys at scale. Our solution, SSH Secure, is built to deliver end-to-end key lifecycle security, provide and gain comprehensive visibility, ensuring that organizations can manage keys confidently without added complexity.

Some of the key features of SSH Secure include:

1. Centralized Visibility and Ownership Mapping

   Through a combination of agent-based and agentless discovery, SSH Secure locates every SSH key across servers and user machines. All keys are stored in a single inventory with ownership and usage details, eliminating orphaned keys, reducing sprawl, and ensuring full accountability across the environment.

2. Key Rotation On-Demand and Scheduled

   SSH Secure allows organizations to rotate SSH keys both on-demand and according to scheduled policies. With a single click, keys can be rotated automatically, ensuring they remain short-lived, reducing the risk of compromise, and providing full visibility into active credentials.

3. Key Revocation On-Demand and Scheduled SSH

   Secure eliminates the risk of non-expiring SSH keys by providing robust key revocation capabilities. Keys associated with departing employees, retired systems, or suspected compromise can be deactivated immediately with just one click. Centralized revocation ensures no forgotten or orphaned keys linger in production environments.

4. Automated Key Lifecycle Orchestration

   Beyond rotation and revocation, SSH Secure automates the complete key lifecycle, covering secure generation, policy-driven rotation, scheduled expiration, and revocation. This reduces manual effort, ensures continuous adherence to security standards, and eliminates operational gaps caused by human error.

5. Ephemeral and Session-Bound Keys

   For sensitive operations, SSH Secure can issue ephemeral session-bound keys that expire automatically. This approach enforces least-privilege access, reduces the impact of compromised credentials, and eliminates long-term exposure from static keys.

6. HSM-Integrated Protection

   All private keys are secured within HSMs, ensuring non-exportability and tamper resistance. Keys are generated using strong cryptographic algorithms such as RSA, ECDSA, and Ed25519, providing both strong protection and resilience against brute-force attacks and efficiency.

7. Policy-Driven Control for Key Operations

   All key operations, such as generation, approval workflows, rotation, and revocation, are enforced through policy-based controls. This ensures consistency across the environment, reduces manual errors, and maintains organization-wide security standards. Policies can be adapted to fit regulatory requirements or customized to support internal governance models.

8. Continuous Monitoring, Auditing, and Compliance Readiness

   SSH Secure provides real-time monitoring of key activities with detailed event logging and built-in anomaly detection. Logs can be integrated with Splunk or Loki-Grafana dashboards for advanced visualization, correlation, and alerting. Flexible audit capabilities include downloadable logs and detailed reports, giving security teams clear insights into key usage and overall posture. Centralized auditing with policy-based alerts enables proactive security management, rapid anomaly detection, and faster incident response.

By implementing these practices, SSH Secure ensures your SSH keys remain tightly controlled, auditable, and secure throughout their lifecycle. This transforms key management from a risky, manual process into a streamlined, compliant, and resilient system.

Conclusion

SSH keys that never expire pose a hidden but serious risk to enterprise security. Forgotten, orphaned, or unmanaged keys can provide persistent access, enabling privilege creep and creating unmonitored entry points across your infrastructure. Without proper oversight, these keys bypass governance and weaken security controls.

Implementing a formal SSH key lifecycle management strategy is the only effective way to mitigate these risks. Practices such as scheduled and on-demand key rotation, revocation, and the use of ephemeral keys reduce long-term exposure, enforce accountability, and ensure that access aligns with the principle of least privilege.

With centralized visibility, policy-driven controls, and automated lifecycle management, organizations can transform SSH key management from a manual, error-prone task into a streamlined, auditable, and resilient system. By addressing key sprawl and enforcing governance, organizations can regain control over SSH authentication, making it more secure, auditable, and easier to manage.