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CVE-2026-27690 – HTTP Request Smuggling – SAP Approuter below v20.10.0

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Summary

CVE-2026-27690 is a critical HTTP Request Smuggling vulnerability (CWE-444) in SAP Approuter (@sap/approuter), the Node.js-based reverse proxy and primary entry point for applications deployed on SAP Business Technology Platform (SAP BTP). Rated 9.1 (Critical) on the CVSS v3.1 scale, the flaw allows an unauthenticated remote attacker to send a specially crafted HTTP request that causes request-response desynchronization, resulting in exposure of other users’ responses and potential service unavailability. All versions of the @sap/approuter npm package below 20.10.0 are affected; SAP has released version 20.10.0 as the fix.

Technical details

  • Root cause: Inconsistent interpretation of HTTP requests (CWE-444) — the front-end and back-end components parse HTTP message boundaries differently, enabling an attacker to smuggle a hidden request inside a legitimate one.
  • Trigger conditions: An unauthenticated attacker sends a specially crafted HTTP request to any publicly reachable SAP Approuter instance. No credentials, privileges, or victim interaction are required.
  • Attack vector: Fully remote and network-accessible (AV:N); low attack complexity (AC:L) — exploitation requires only a crafted HTTP request, with no special configuration or race condition needed.
  • Impact: Successful exploitation causes request-response desynchronization, which can expose HTTP responses destined for other users (high confidentiality impact) and can render the Approuter service unavailable (high availability impact). There is no integrity impact.

Affected software

  • SAP Approuter (@sap/approuter npm package) — all versions below 20.10.0

Severity

CVSS v3.1 Base Score: 9.1 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Mitigation and recommended actions

  • Immediate – apply the vendor patch: Update the @sap/approuter npm package to version 20.10.0 or later, which resolves this vulnerability per SAP Security Note 3720138.
  • If immediate patching is not feasible: Restrict inbound network access to SAP Approuter endpoints at the perimeter (e.g., firewall or WAF rules) to limit exposure while the patch is scheduled, prioritizing any internet-facing deployments.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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