How severe is CVE-2026-106491?

CVE-2026-106491 has a CVSS score of 6.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-106491?

CVE-2026-106491 affects the following packages: @backstage/plugin-proxy-backend (npm). Ecosystems affected: npm.

How do I fix CVE-2026-106491?

Update @backstage/plugin-proxy-backend to 0.6.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-106491 is resolved across your whole dependency graph.

How do I detect CVE-2026-106491 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @backstage/plugin-proxy-backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-106491 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Is CVE-2026-106491 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-106491 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-106491?

CVE-2026-106491 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 18th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-106491?

CVE-2026-106491 is classified as Improper Input Validation (CWE-20), Path Traversal (CWE-22). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-106491 published, and has it been updated?

CVE-2026-106491 was published on October 6, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

CVE-2026-106491 — @backstage/plugin-proxy-b…

MEDIUMFix: backstage/backstage@233287d

CVE-2026-106491 is a medium-severity (CVSS 6.4) Improper Input Validation vulnerability in @backstage/plugin-proxy-backend. A fix is available for @backstage/plugin-proxy-backend — see the affected versions and patch details below.

Backstage: Improper input validation in proxy-backend

Also known asGHSA-9ghw-48h5-v2w5

Published

Oct 6, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-106491.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs18th percentile — riskier than 18% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-106491 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

📦@backstage/plugin-proxy-backend

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

Description

Backstage is an open framework for building developer portals. Prior to 0.6.17, the @backstage/plugin-proxy-backend package is affected by improper input validation in proxy-backend. An authenticated Backstage user could craft a request URL that causes the proxy-backend to forward the request to a path outside the configured base path on the target server. This is limited to target servers already configured as proxy endpoints and requires Backstage authentication by default. This issue is fixed in version 0.6.17.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@backstage/plugin-proxy-backend`	all versions	0.6.17`npm install @backstage/plugin-proxy-backend@0.6.17`

Affected Products

2 products · 2 configurations

Application

backstagelinuxfoundation

< 1.54.6

range

Application

backstage\/plugin-proxy-backendlinuxfoundation

< 0.6.17

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @backstage/plugin-proxy-backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @backstage/plugin-proxy-backend to 0.6.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-106491 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Red Hat rates the impact of this vulnerability as Moderate because exploitation requires valid authenticated access to the developer portal and path traversal is confined solely to destinations already configured as proxy endpoints rather than arbitrary internal or external targets. Consequently, an attacker cannot…

Workaround published by Red Hat

To mitigate this issue, deploy an upstream reverse proxy or Web Application Firewall (WAF) in front of the Backstage / Red Hat Developer Hub backend configured to normalize incoming URI paths and block path traversal sequences before requests reach the application.

Source: Red Hat security advisory for CVE-2026-106491 (CC BY 4.0)

Frequently Asked Questions

### Impact An authenticated Backstage user could craft a request URL that causes the proxy-backend to forward the request to a path outside the configured base path on the target server. This is limited to target servers already configured as proxy endpoints and requires Backstage authentication by default. ### Patches Patched in `@backstage/plugin-proxy-backend` version `0.6.17` ### Workarounds - Deploy a reverse proxy or WAF in front of Backstage that normalizes request paths before they reach the backend.