Executive brief
Cap-go is a service used for managing and deploying mobile app updates. A security flaw allows users with restricted, read-only access to prematurely cancel active app builds by simply disconnecting from a log stream. This can be used by malicious insiders or compromised accounts to disrupt development workflows and prevent teams from successfully building or deploying their software.
Technical details
A privilege inversion vulnerability exists in the 'GET /build/logs/:jobId' endpoint of Cap-go. While the endpoint itself is restricted to 'app.read_logs' permissions, it registers an abort listener on the Server-Sent Events (SSE) stream that unconditionally triggers 'cancelBuildOnDisconnect()'. This function executes the cancellation using a privileged server-side 'BUILDER_API_KEY', bypassing the 'app.build_native' write permission check enforced on the standard cancellation endpoint. An attacker with a valid read-only API key can disrupt CI/CD workflows by initiating a log stream and abruptly dropping the TCP connection, causing the server to terminate the associated build job. This issue is resolved in version 12.128.2.
Affected products
- Cap-go capgo < 12.128.2
Timeline
- 2026-05-07: advisory: GitHub Security Advisory GHSA-95g7-xwwx-j737 published
- 2026-06-22: disclosed: CVE-2026-56280 published to NVD