Executive brief
Capgo, a platform for managing mobile app updates, contains a security flaw in its build system. An authorized user could bypass security restrictions to access internal administrative tools by manipulating web addresses. This could allow an attacker to interfere with the app building process, access sensitive internal data, or potentially run unauthorized code within the build environment.
Technical details
A path traversal vulnerability exists in the Capgo builder upload proxy (specifically in supabase/functions/_backend/public/build/upload.ts). The application appends user-controlled path segments to the builder upload URL without sanitization. When the request is processed by the WHATWG URL parser in the fetch() API, traversal sequences like '/../' are normalized, allowing an attacker to reach internal administrative endpoints. Because the proxy automatically attaches a privileged BUILDER_API_KEY header to these requests, an authenticated user with build permissions can achieve server-side privilege escalation and SSRF. This allows for the manipulation of build jobs and potential execution of attacker-controlled workloads. The issue is fixed in version 12.128.2.
Affected products
- Capgo Capgo before 12.128.2
Timeline
- 2026-03-17: advisory: GitHub Security Advisory published by maintainers
- 2026-06-30: disclosed: NVD and VulnCheck publication date
- 2026-06-30: patched: Fix confirmed in version 12.128.2