Secure authentication

What the requirement asks

Secure authentication technologies and procedures are to be put in place, driven by the information access restrictions and the access control policy. Purpose: authenticate users and other entities securely whenever they are given access to systems, applications and services. Guidance: choose an authentication technique suited to proving the claimed identity of users, software, messages and other entities, with strength matched to the classification of what is being accessed. When identity must be proven strongly, rely on something other than a password, for example certificates, smart cards, hardware tokens or biometric traits. Access to critical systems should use multi-factor authentication combining something known, held and inherent, which can be extended with rule-based step-up when access comes from an unusual location, device or time. Compromised biometric data should be invalidated, and because biometrics can fail in some conditions (moisture, ageing) at least one alternative technique should be available. Log-on should be designed to minimize unauthorized access by: not revealing sensitive system or application details until log-on succeeds; showing a notice that only authorized users may access the system; giving no help during log-on that could aid an intruder, such as saying which part of the input was wrong; validating the log-on only once all input is complete; resisting brute force through CAPTCHA, forced reset after a set number of failures or lockout; logging failed and successful attempts; raising a security event and alerting the user and administrators when a possible attack on log-on controls is seen; showing or sending separately, after success, when the last successful log-on happened and any failed tries since then; hiding passwords as typed, unless this must be relaxed for accessibility or to avoid repeated lockouts; never sending passwords in clear text across networks; ending sessions after a period of inactivity, especially in public or external locations and on endpoints; and limiting connection times for high-risk applications. Other information: ISO/IEC 29115 covers entity authentication assurance. In the ISMS the control is compared with the controls determined in risk treatment and recorded in the Statement of Applicability as included or excluded, with the reason and the implementation status.

What the guidance adds

Secure authentication is expected to be strong and usable. The guidance asks for the method, the enrolment, the recovery and the resistance to common attacks.

What good looks like

Put the control in the Statement of Applicability with an owner, a status and the risk it treats. Then keep an authentication standard linking required authentication strength to information classification and system criticality and one live sample together.

Evidence an assessor asks for

• Authentication strengthAn authentication standard linking required authentication strength to information classification and system criticality
• Authentication strengthMFA configuration and coverage reports for critical systems, remote access and privileged access, including conditional or risk-based rules
• Authentication strengthLog-on configuration showing warning banners, generic error messages, lockout or throttling after failed attempts and masked password entry
• Authentication strengthAuthentication logs recording successful and failed attempts, with alerting on suspected brute force
• Authentication strengthSession timeout and connection time limit settings for high-risk applications and locations
• Authentication strengthEvidence that passwords are not transmitted in clear text, for example TLS enforcement on log-on endpoints

The question an assessor will ask

An assessor will ask for an authentication standard linking required authentication strength to information classification and system criticality, then trace it to the system it protects. For A.8.5 the test is whether that record ties to a live sample, not whether the control is named in a policy.

Common gaps

• MFA is enabled for some critical systems but legacy protocols allow bypass
• Error messages reveal whether the username or the password was wrong
• No lockout or rate limiting exists on internet-facing log-on pages
• Biometric authentication has no fallback method

Before the next audit

Before the next audit, check one live sample for this gap: mfa is enabled for some critical systems but legacy protocols allow bypass.