CVE-2026-39857: ApostropheCMS information disclosure via choices and counts query parameters

Executive brief

ApostropheCMS is a content management system used to build and manage websites. A vulnerability in its web interface allows unauthenticated visitors to bypass security restrictions and view sensitive data fields that were intended to be hidden. This could lead to the exposure of internal status values, categories, or other restricted information stored within the system.

Technical details

An information disclosure vulnerability exists in ApostropheCMS due to the way the REST API handles 'choices' and 'counts' query parameters. While the main API query enforces field restrictions via 'publicApiProjection' using MongoDB projections, the 'choices' and 'counts' builders use a separate code path that utilizes the MongoDB 'distinct' operation. Because 'distinct' does not respect projections, unauthenticated attackers can extract all unique values and document counts for any schema field, including those explicitly excluded from public view or protected by 'viewPermission'. This affects both the piece-type and page REST APIs. The issue is fixed in version 4.29.0.

Affected products

• ApostropheCMS apostrophe <= 4.28.0

Timeline

• 2026-04-15: patched: Fixed in version 4.29.0
• 2026-04-15: disclosed
• 2026-04-16: advisory

References

• https://api.github.com/users/offset
• https://github.com/offset
• https://api.github.com/users/offset/gists%7B/gist_id%7D
• https://api.github.com/users/offset/repos
• https://avatars.githubusercontent.com/u/114768995?v=4
• https://api.github.com/users/offset/events%7B/privacy%7D