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CVE-2026-54734 – Server-Side Request Forgery (SSRF) – Prebid Server Java < 3.43.0

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Summary

CVE-2026-54734 is a critical Server-Side Request Forgery (SSRF) vulnerability affecting Prebid Server Java, the server-side implementation of the Prebid header bidding platform. Certain bidder adapters interpolate user-supplied bid-request parameters directly into outbound HTTP request URLs without validating the resulting domain or path segment, allowing an unauthenticated attacker to redirect server-side requests to arbitrary destinations. The flaw carries a maximum CVSS v3.1 score of 10.0 and affects all versions prior to 3.43.0.

Technical details

  • Root cause: Certain bidder adapters build outbound bid-request URLs by concatenating attacker-controllable parameters without routing them through the platform’s HttpUtil domain/path validation logic.
  • Trigger conditions: An attacker submits a crafted bid request containing malicious parameter values (e.g., a manipulated hostname or path segment) that get embedded into the URL the server subsequently requests.
  • Attack vector: Network-based, requires no authentication and no user interaction (CVSS AV:N/AC:L/PR:N/UI:N).
  • Impact: The server can be coerced into sending HTTP requests to unintended destinations — potentially reaching internal network services, cloud metadata endpoints, or other sensitive endpoints reachable from the server’s network position — resulting in high confidentiality, integrity, and availability impact, with a changed scope (S:C) indicating impact beyond the vulnerable component.

Affected software

  • Prebid Server Java (prebid/prebid-server-java) versions prior to 3.43.0

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade Prebid Server Java to version 3.43.0 or later, which fixes the vulnerable URL-construction logic in the affected bidder adapters.
  • If immediate patching is not feasible: Disable or remove the vulnerable bidder adapter integrations from your Prebid Server configuration until the upgrade can be applied, and restrict the server’s outbound network access (e.g., via egress filtering) to reduce exposure to internal services and metadata endpoints.

References

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