CVE-2026-27886: Strapi may leak sensitive data via relational filtering due to lack of query sanitization

Summary of CVE-2026-27886 Vulnerability Details

• CVE: CVE-2026-27886
• CVSS v3.1 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N (9.3 — Critical)
• Affected Versions: @strapi/strapi <=5.36.1
• How to Patch: Immediately update your Strapi to >=5.37.0

Description of CVE-2026-27886

Strapi versions prior to 5.37.0 did not sufficiently sanitize query parameters when filtering content via relational fields. An unauthenticated attacker could use the where query parameter on any publicly-accessible content-type with an updatedBy (or other admin-relation) field to perform a boolean-oracle attack against private fields on the joined admin_users table, including the resetPasswordToken field. Extracting an admin reset token via this oracle made full administrative account takeover possible without authentication.

When a filter such as where[updatedBy][resetPasswordToken][$startsWith]=a was applied to a public Content API endpoint, the underlying query generation performed a LEFT JOIN against the admin_users table and emitted a WHERE clause referencing the joined column. The query parameter sanitization layer did not block operator chains that traversed into relational target schemas the caller had no read permission on, allowing the response count to be used as a one-bit oracle on any admin-table field.

The patch introduces explicit query-parameter sanitization at the controller and service boundary via three new primitives: strictParam, addQueryParams, and addBodyParams. Operator chains that traverse into restricted relational targets are now rejected before reaching the database.

IoC's for CVE-2026-27886

Indicators that an instance running an unpatched version may have been exploited:

• Server access logs containing query strings traversing into admin-relation private fields. Regex: \?(.*&)?where\[(updatedBy|createdBy|publishedBy)\]\[(email|password|resetPasswordToken|confirmationToken|firstname|lastname|preferedLanguage)\]\[\$(startsWith|contains|eq|gt|lt|ge|le|in|notIn|notNull|null)\]=
• High volume of public Content API requests from a single IP iterating through a hex alphabet (0-9, a-f) on the same content-type endpoint with progressively-longer filter values
• Subsequent POST /admin/reset-password calls using a reset token that the legitimate admin did not request
• Successful admin password change immediately following a burst of public Content API requests with where[updatedBy] query parameters
• Sustained burst of identical-shape requests with only the trailing character of the filter value varying

Credit

Discovered by: James Doll - WildWest CyberSecurity Contact: [email protected] Website: https://wildwestcyber.com LinkedIn: https://www.linkedin.com/in/james-doll-273a61243