Nitro has a proxy scope bypass via percent-encoded path traversal in routeRules

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-44373: 0.45% estimated exploitation activity in the next 30 days; percentile 39.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

A proxy route rule like: is intended to limit the proxy to URLs under /api/orders/. Before the patch, an attacker could bypass that scope by sending percent-encoded path traversal (..%2f) in the URL, causing Nitro to forward a request that the upstream resolved outside the configured scope. Example exploit: Nitro sees ..%2f as opaque characters at match time, the /api/orders/ rule matched, and the raw path was forwarded to the upstream as /orders/..%2fadmin/config.json. An upstream that decodes %2F to / then resolved .. and can serve /admin/config.json outside the intended scope. Are you affected? Users may be affected if ALL of the following are true: 1. Their project uses Nitro's routeRules with a proxy entry ({ proxy: { to: "..." } }). 2. The proxy to value uses a / wildcard suffix to forward sub-paths. 3. The upstream behind the proxy decodes %2F as / before routing or filesystem lookup. 4. Proxy route rules are not handled natively at CDN (nitro v3 and vercel) Whether the bypass…

Published by the source

6 May 2026, 23:01 UTC

Last modified by the source

14 May 2026, 20:48 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5w89-w975-hf9q

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-5w89-w975-hf9q

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-44373

Advisory: Nitro has a proxy scope bypass via percent-encoded path traversal in `routeRules`
IDs: CVE-2026-44373, GHSA-5w89-w975-hf9q
Record: https://patchnext.com/advisories/cve-2026-44373 (revision 2, source checked 26 Oct 2026, 12:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nitro 3.0.260429-beta; nitropack 2.13.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm nitro: affected < 3.0.260429-beta; fixed in 3.0.260429-beta
- npm nitropack: affected < 2.13.4; fixed in 2.13.4

## Suggested inspection (read-only)
- `npm ls nitro --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls nitropack --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nitro, nitropack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5w89-w975-hf9q (OSV record GHSA-5w89-w975-hf9q lists affected ranges: npm nitro >=0 =0 <2.13.4 (fixed))
- Verified: https://github.com/advisories/GHSA-5w89-w975-hf9q (GitHub-reviewed advisory GHSA-5w89-w975-hf9q lists affected ranges: npm nitro >=0 =0 <2.13.4)

Commands are suggestions: review each one before running it.