Craft CMS Allows TOTP Token To Stay Valid After Use

Craft CMS 5 allows reuse of TOTP tokens multiple times within the validity period.

Impact

An attacker is able to re-submit a valid TOTP token to establish an authenticated session. This requires that the attacker has knowledge of the victim's credentials.

A TOTP token can be used multiple times to establish an authenticated session. RFC 6238 insists that an OTP must not be used more than once.

> The verifier MUST NOT accept the second attempt of the OTP after the successful validation has been issued for the first OTP, which ensures one-time only use of an OTP.

The OWASP Application Security Verification Standard v4.0.3 (ASVS) reiterates this property with requirement 2.8.4.

> Verify that time-based OTP can be used only once within the validity period.

It should also be noted that the validity period of an TOTP token is 2 minutes. This makes a successful brute force attack more likely, since the four tokens are valid at the same time.

Patches

This has been patched in Craft 5.2.3.

References:

https://github.com/sbaresearch/advisories/tree/public/2024/SBA-ADV 2024061701_CraftCMS_TOTP_Valid_After_Use

https://github.com/craftcms/cms/releases/tag/5.2.3