Fleet: Unauthenticated download of in-house iOS app binaries via predictable URLs

Summary

Two endpoints serving in-house iOS application packages and manifests in Fleet's enterprise tier are reachable without a hard-to-guess token in the URL, allowing an unauthenticated attacker who can reach the Fleet server to download an in-house IPA by guessing sequential title identifiers.

Impact

By design, Apple's InstallEnterpriseApplication MDM command requires that the manifest URL be reachable by the managed device without a Fleet session, so these endpoints cannot enforce session-based authentication. Fleet's legacy MDM installer path mitigates this by embedding a random, hard-to-guess token in the URL; the in-house iOS app endpoints (added later) were always intended to use the same time-limited-token pattern but the mitigation was not yet in place.

The result is read-only disclosure of in-house IPA binaries and their metadata (bundle identifier, version, name) that an operator has deployed through Fleet. This is enterprise-tier only — the free tier returns fleet.ErrMissingLicense. There is no privilege escalation, write access, or impact on hosts not managed by Fleet.

Workarounds

If an immediate upgrade is not possible:

• Restrict network access to the Fleet server to trusted networks, as is typical for MDM deployments.
• Remove in-house iOS apps that contain sensitive material from Fleet; in-house app IPAs are intentionally reachable by managed devices and should not be relied on as a confidential distribution channel.
• Where available, configure CloudFront URL signing for software installers to limit the validity window of issued binary URLs.

For more information

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Credits

We thank @offset for responsibly reporting this issue.