CVE-2026-105770: Octo STS discloses trust policy contents to unauthorized callers via Exchange error messages

Vulnerability summary

CVE-2026-105770 is a medium (CVSS 5.3) vulnerability in octo-sts app. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 17.3% of scored vulnerabilities.

Timeline

1. 03-11-2026
   PublishedVulnerability first disclosed.

Description

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.

• CWE-209Generation of Error Message Containing Sensitive InformationThe product generates an error message that includes sensitive information about its environment, users, or associated data.