Nitro PDF Pro before 14.43 for Windows contains a NULL pointer dereference vulnerability in the JavaScript implementation of app.alert(). When app.alert() is called with more than one argument and the first argument evaluates to null (for example, app.alert(app.activeDocs, true) when app.activeDocs is null), the engine routes the call through a fallback path intended for non-string arguments. In this path, jsValueToString() is invoked on the null value and returns an invalid string pointer, which is then passed to JSGetStringChars() without validation. Dereferencing this pointer leads to an access violation and application crash when opening a crafted PDF. For example, 14.41.1.4 and 14.42.0.34 have been reported as vulnerable.

Nitro PDF Pro for Windows 14.41.1.4 contains a heap use-after-free vulnerability in the implementation of the JavaScript method this.mailDoc(). During execution, an internal XID object is allocated and then freed prematurely, after which the freed pointer is still passed into UI and logging helper functions. Because the freed memory region may contain unpredictable heap data or remnants of attacker-controlled JavaScript strings, downstream routines such as wcscmp() may process invalid or stale pointers. This can result in access violations and non-deterministic crashes.

A redirect route rule like:

ts routeRules: { "/legacy/": { redirect: "/" } }

is intended to rewrite paths within the same host. Before the patch, an attacker could turn the rewrite into a cross-host redirect by sliding an extra slash in after the rule prefix. Example exploit:

GET /legacy//evil.com

Nitro stripped /legacy from the matched pathname and joined the remainder against the rule's target. The remainder was //evil.com, which the join preserved verbatim, so Nitro responded with Location: //evil.com. Browsers resolve //evil.com as a protocol-relative URL against the current scheme, sending the user to https://evil.com.

Are you affected?

Users may be affected if all of the following are true:

1. Their project uses Nitro's routeRules with a redirect entry. 2. The target uses a / wildcard suffix to forward sub-paths (e.g. redirect: "/", redirect: "/new/", proxy: { to: "http://upstream/" }). 3. The redirect rule is not handled natively at the CDN layer. The vercel, netlify, cloudflare-pages, and edgeone presets translate routeRules.redirect into platform config (vercel.json, redirects, EdgeOne v3 config) and serve the redirect at the edge — those deployments bypass the Nitro runtime entirely and are not affected. Every other preset executes the redirect through the Nitro runtime and can be vulnerable.

Impact

Open redirect from any host serving Nitro with a wildcard redirect rule. The redirect target is fully attacker-controlled, the URL looks legitimate (it starts with the victim's domain), and the browser silently follows it.

Patched versions

Upgrade to one of:

- 2.13.4 or later (or upgrade lockfile with latest ufo 1.6.4+) - 3.0.260429-beta or later (https://github.com/nitrojs/nitro/pull/4236)

The fix has two parts:

1. ufo is bumped to ^1.6.4 (unjs/ufo@5cd9e67), which collapses any run of leading slashes to a single / inside withoutBase. This covers the typical "/scope/" rule. 2. The Nitro runtime additionally collapses leading // before joining when the rule path itself is / (in rare case which case withoutBase is never called and the raw pathname flows straight into joinURL("", …)).

A proxy route rule like:

ts routeRules: { "/api/orders/": { proxy: { to: "http://upstream/orders/" } } }

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:

GET /api/orders/..%2fadmin%2fconfig.json

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 actually leaks data depends on the upstream. Modern JS frameworks keep %2F opaque per RFC 3986 and are safe by construction.

- Safe examples: H3 v2, Express v5, Hono v4 — modern JS frameworks keep %2F opaque per RFC 3986. - Vulnerable examples: naive imlementations that decodes the URL, static file servers, CGI dispatchers, Python os.path-based routing, anything sitting behind another layer that decodes %2F (common in microservice meshes).

Impact

Any HTTP path reachable from the Nitro server to the upstream could be requested, regardless of the configured / scope. In typical deployments (API gateway, BFF, microservice proxy) this could expose internal admin endpoints, secrets endpoints, or other services the developer believed the scope rule fenced off.

Patched versions

Upgrade to one of:

- 2.13.4 or later (https://github.com/nitrojs/nitro/pull/4223) - 3.0.260429-beta or later (https://github.com/nitrojs/nitro/pull/4222)

The fix canonicalizes the incoming pathname before building the upstream URL and rejects requests with 400 Bad Request if the resolved path would escape the rule's base. The bytes forwarded upstream are unchanged when the request is allowed.

Note: the fix assumes the upstream does not double-decode percent-encoding. If your upstream decodes twice (%252F → %2F → /), it remains your responsibility to harden it. Single-decode is standard.

Credits

Reported by @mHe4am (@he4am on HackerOne) via the Vercel Open Source program.

A NULL pointer dereference in Nitro PDF Pro for Windows v14.41.1.4 allows attackers to cause a Denial of Service (DoS) via a crafted XFA packet.

Nitro PDF Pro before 13.70.8.82 and 14.x before 14.26.1.0 allows Local Privilege Escalation in the MSI Installer because custom actions occur unsafely in repair mode. CertUtil is run in a conhost.exe window, and there is a mechanism allowing CTRL+o to launch cmd.exe as NT AUTHORITY\SYSTEM.