CVE-2026-27128: Craft CMS's race condition in Token Service potentially allows for token usage greater than the token limit
A Time-of-Check-Time-of-Use (TOCTOU) race condition exists in Craft CMS’s token validation service for tokens that explicitly set a limited usage. The getTokenRoute() method reads a token’s usage count, checks if it’s within limits, then updates the database in separate non-atomic operations. By sending concurrent requests, an attacker can use a single-use impersonation token multiple times before the database update completes.
To make this work, an attacker needs to obtain a valid user account impersonation URL with a non-expired token via some other means and exploit a race condition while bypassing any rate-limiting rules in place.
For this to be a privilege escalation, the impersonation URL must include a token for a user account with more permissions than the current user.
References
https://github.com/craftcms/cms/commit/3e4afe18279951c024c64896aa2b93cda6d95fdf
Other sources
Craft is a content management system (CMS). In versions 4.5.0-RC1 through 4.16.18 and 5.0.0-RC1 through 5.8.22, a Time-of-Check-Time-of-Use (TOCTOU) race condition exists in Craft CMS’s token validation service for tokens that explicitly set a limited usage. The getTokenRoute() method reads a token’s usage count, checks if it’s within limits, then updates the database in separate non-atomic operations. By sending concurrent requests, an attacker can use a single-use impersonation token multiple times before the database update completes. To make this work, an attacker needs to obtain a valid user account impersonation URL with a non-expired token via some other means and exploit a race condition while bypassing any rate-limiting rules in place. For this to be a privilege escalation, the impersonation URL must include a token for a user account with more permissions than the current user. Versions 4.16.19 and 5.8.23 patch the issue.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27128?
CVE-2026-27128 has been rated as a high severity vulnerability due to its potential impact on token usage integrity.
How do I fix CVE-2026-27128?
To fix CVE-2026-27128, upgrade Craft CMS to version 5.8.23 or 4.16.19.
Which versions are affected by CVE-2026-27128?
CVE-2026-27128 affects Craft CMS versions between 5.0.0-RC1 and 5.8.22, as well as versions between 4.5.0-RC1 and 4.16.18.
What impact does CVE-2026-27128 have on my Craft CMS installation?
CVE-2026-27128 could lead to unauthorized token usage through a race condition issue.
Is there a workaround for CVE-2026-27128 before upgrading?
While immediate fixes are not provided, limiting access to the token validation service may help minimize risk until an upgrade is performed.