Auth bypass in @Backstage Plugin-Proxy-Backend

CVE-2026-106456

Backstage is an open framework for building developer portals. From 0.5.0 until 0.6.18, the @backstage/plugin-proxy-backend package is affected by inconsistent credential enforcement for overlapping proxy routes. An operator can configure overlapping proxy paths with different credential requirements. When a parent path permits unauthenticated access and a nested path requires credentials, the parent exemption can also cover requests handled by the nested proxy. An unauthenticated caller may therefore reach the nested upstream through Backstage, including with static upstream credentials configured for that proxy. This issue is fixed in version 0.6.18.

Vulnerability class: Broken Access Control

Published .

CVSS v3 metric

CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-106456?
CVE-2026-106456 is a medium-severity vulnerability in @Backstage Plugin-Proxy-Backend, classified under Incorrect Authorization. CVSS score: 4.8/10. Published 2026-10-06.
How severe is CVE-2026-106456?
Medium severity. CVSS v3 base score is 4.8 out of 10.