Octo STS (github.com/octo-sts/app) before 0.11.2 returns trust policy configuration to callers whose OIDC token does not satisfy that policy. TrustPolicy.CheckToken included the policy's issuer, subject and audience values or patterns and claim_pattern names and regular expressions in its PermissionDenied errors, which Exchange returned verbatim. Exchange also selected the GitHub App installation before checking the token, so errors from resolving the policy's app or app_pattern pin were returned to callers the policy does not trust. An attacker who holds any validly signed OIDC token, such as a GitHub Actions token from a repository they own, and who knows or guesses a target owner/repo and identity name can read that policy's matching rules, even when the policy is stored in a private repository. These rules often name internal repositories, branches, environments or cloud account identifiers. The issue does not allow minting tokens or bypassing a trust policy. This issue is fixed in 0.11.2.
None for self-hosted deployments other than upgrading.
Upgrade to Octo STS 0.11.2 or later. The token is now checked against the trust policy immediately after the policy is loaded and before installation selection or app pin resolution. On a mismatch the detailed reason is logged and recorded on the operator audit event, and the caller receives only a generic "PermissionDenied: token does not match trust policy". Policies that exist but cannot be read, parsed or compiled now return the same NotFound response as a missing policy. Users of the hosted service are protected once the fix is deployed.