Abusing Misconfigured API Gateways in SaaS Supply Chains

During a SaaS supply-chain engagement we chained API gateway misconfigurations with scope misalignment to escalate from low-privilege access into privileged partner functions.

The integration gateway accepted legacy tokens signed by deprecated keys. By replaying these tokens with crafted audiences we bypassed policy enforcement and reached internal partner endpoints. A lack of response signature validation enabled payload tampering without detection.

Key Takeaways

Security teams should rotate signing keys, ensure scopes are validated against current contracts, and reject tokens that fail freshness checks. Additionally, mutual TLS between gateway and upstream services would have prevented replay.

Our remediation guidance included a hardened gateway configuration template, automated scope reconciliation, and partner attestation workflows aligned with OWASP API Security Top 10 recommendations.