patrickjuchli · patrickjuchli · Jul 25, 2026 · Jul 25, 2026 · Jul 25, 2026
diff --git a/.github/workflows/nodejs.yml b/.github/workflows/nodejs.yml
@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [20.x, 22.x, 24.x, 25.x]
+        node-version: [20.x, 22.x, 24.x, 25.x, 26.x]
 
     steps:
       - uses: actions/checkout@v6

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Fixed: Implicit FTPS transfers against servers requiring TLS session reuse failed with "425 ... TLS session of data connection not resumed" on Node.js with the CVE-2026-48934 fix (22.23.0+, 24.17.0+, 26.3.1+).
+
 ## 6.0.1
 
 - Fixed: Use and renew TLS 1.3 session tickets for data connections.

diff --git a/src/Client.ts b/src/Client.ts
@@ -143,6 +143,15 @@ export class Client {
      */
     connectImplicitTLS(host = "localhost", port = 21, tlsOptions: TLSConnectionOptions = {}): Promise<FTPResponse> {
         this.ftp.reset()
+        // Remember the host identity so future data connections can resume this TLS
+        // session. Since Node.js v24.17.0 (CVE-2026-48934) a reusable TLS session is
+        // bound to the host it was authenticated for, and resumption is refused when
+        // the resuming connection's identity (servername ?? host ?? socket._host)
+        // differs. Data connections connect to the PASV/EPSV target, so without an
+        // explicit host they'd resume under a different (or missing) identity and the
+        // server would report the session as not resumed. This mirrors what `access`
+        // already does for explicit TLS, see https://github.com/patrickjuchli/basic-ftp/issues/166.
+        tlsOptions.host = tlsOptions.host ?? host
         this.ftp.socket = connectTLS(
             port,
             host,

diff --git a/test/implicitTlsReuseSpec.js b/test/implicitTlsReuseSpec.js
@@ -0,0 +1,203 @@
+const { describe, it, beforeEach, afterEach } = require("node:test");
+const assert = require("assert");
+const crypto = require("crypto");
+const tls = require("tls");
+const { Readable } = require("stream");
+const { Client } = require("../dist");
+
+// Self-signed cert for 127.0.0.1 / localhost, used only by these tests.
+const KEY = `-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----`;
+const CERT = `-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`;
+
+// Minimal implicit-FTPS server that REQUIRES the data connection to resume the
+// control connection's TLS session — the behaviour of FileZilla Server and of
+// ProFTPD without NoSessionReuseRequired. The control and data listeners share
+// TLS ticket keys so a correctly-presented session resumes across them; if the
+// data connection did NOT resume (server-side isSessionReused() === false) the
+// STOR is rejected with 425, exactly as a real server reports it.
+//
+// This lets a plain `node --test` run reproduce the CVE-2026-48934 regression:
+// on an affected runtime (Node 22.23.0+, 24.17.0+, 26.3.1+) an unpinned data
+// connection falls back to a "localhost" identity that doesn't match the
+// control's "127.0.0.1", so Node refuses to resume, the server answers 425 and
+// the upload rejects. connectImplicitTLS() pinning the host fixes it.
+class ImplicitReuseServer {
+    constructor() {
+        const tlsOptions = { key: KEY, cert: CERT, ticketKeys: crypto.randomBytes(48) };
+        this.lastDataReused = null;
+        this._pending = null;
+        this.controlServer = tls.createServer(tlsOptions, sock => this._handleControl(sock));
+        this.dataServer = tls.createServer(tlsOptions, sock => this._handleData(sock));
+    }
+
+    listen() {
+        return Promise.all([
+            new Promise(r => this.controlServer.listen(0, "127.0.0.1", r)),
+            new Promise(r => this.dataServer.listen(0, "127.0.0.1", r)),
+        ]);
+    }
+
+    get port() { return this.controlServer.address().port; }
+    get dataPort() { return this.dataServer.address().port; }
+
+    close() {
+        this.controlServer.close();
+        this.dataServer.close();
+    }
+
+    _handleData(sock) {
+        const state = this._pending;
+        const reused = sock.isSessionReused();
+        this.lastDataReused = reused;
+        if (state) {
+            state.dataSocket = sock;
+            state.dataReused = reused;
+        }
+        sock.on("data", () => {});
+        sock.on("end", () => { if (state) { state.dataEnded = true; if (state.onEnd) state.onEnd(); } });
+        sock.on("error", () => {});
+    }
+
+    _handleControl(control) {
+        const state = { dataSocket: null, dataReused: null, dataEnded: false, onEnd: null };
+        this._pending = state;
+        control.on("error", () => {});
+        control.write("220 Welcome\r\n");
+        let buffer = "";
+        control.on("data", chunk => {
+            buffer += chunk.toString("latin1");
+            let idx;
+            while ((idx = buffer.indexOf("\r\n")) >= 0) {
+                const line = buffer.slice(0, idx);
+                buffer = buffer.slice(idx + 2);
+                this._onCommand(control, line, state);
+            }
+        });
+    }
+
+    _onCommand(control, line, state) {
+        const cmd = line.split(" ")[0].toUpperCase();
+        switch (cmd) {
+            case "USER": control.write("331 Need password\r\n"); break;
+            case "PASS": control.write("230 Logged in\r\n"); break;
+            case "FEAT": control.write("211 End\r\n"); break;
+            case "TYPE": case "STRU": case "PBSZ": case "PROT": case "OPTS":
+                control.write("200 OK\r\n"); break;
+            case "EPSV":
+                control.write(`229 Entering Extended Passive Mode (|||${this.dataPort}|)\r\n`); break;
+            case "STOR": this._handleStor(control, state); break;
+            case "QUIT": control.write("221 Bye\r\n"); break;
+            default: control.write("500 Unknown command\r\n");
+        }
+    }
+
+    _handleStor(control, state) {
+        const proceed = () => {
+            if (!state.dataReused) {
+                // The core of the test: a non-resumed data connection is rejected.
+                control.write("425 Unable to build data connection: TLS session of data connection not resumed.\r\n");
+                if (state.dataSocket) state.dataSocket.destroy();
+                return;
+            }
+            control.write("150 Opening data connection\r\n");
+            const finish = () => control.write("226 Transfer complete\r\n");
+            if (state.dataEnded) finish();
+            else state.onEnd = finish;
+        };
+        // The data connection is opened during prepareTransfer, before STOR, but
+        // guard against ordering races on slower machines.
+        if (state.dataSocket) proceed();
+        else {
+            const timer = setInterval(() => {
+                if (state.dataSocket) { clearInterval(timer); proceed(); }
+            }, 5);
+        }
+    }
+}
+
+describe("Implicit TLS data-connection session reuse", () => {
+
+    let server, client;
+
+    beforeEach(async () => {
+        server = new ImplicitReuseServer();
+        await server.listen();
+        client = new Client(4000);
+    });
+
+    afterEach(() => {
+        client.close();
+        server.close();
+    });
+
+    // Regression guard for CVE-2026-48934. On affected Node runtimes this upload
+    // rejects with 425 unless connectImplicitTLS() pins the control host so the
+    // data connection resumes the session. On unaffected runtimes (e.g. the EOL
+    // 25.x line) resumption happens anyway and this simply passes.
+    it("resumes the control session on the data connection (upload succeeds)", async () => {
+        await client.access({
+            host: "127.0.0.1",
+            port: server.port,
+            user: "test",
+            password: "test",
+            secure: "implicit",
+            secureOptions: { ca: CERT, rejectUnauthorized: true }
+        });
+
+        await assert.doesNotReject(
+            () => client.uploadFrom(Readable.from(["hello reuse"]), "reuse-test.txt"),
+            "upload must not be rejected — the data connection has to resume the TLS session"
+        );
+
+        assert.strictEqual(
+            server.lastDataReused,
+            true,
+            "server must observe the data connection as a resumed TLS session"
+        );
+    });
+});
diff --git a/test/implicitTlsSpec.js b/test/implicitTlsSpec.js
@@ -0,0 +1,102 @@
+const { describe, it, beforeEach, afterEach } = require("node:test");
+const assert = require("assert");
+const tls = require("tls");
+const { Client } = require("../dist");
+
+// Self-signed cert for 127.0.0.1 / localhost, used only by these tests.
+const KEY = `-----BEGIN PRIVATE KEY-----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+FyRB+Mp6GQKBgA9w8zKD1Y5wYzCAkv6Gj268uOPw706DuKdBvoYYbOSEgGOWT5bm
+ZB4NijYpdJCgBGIBkub7e1WmrJ+ROtXsjG35sDyedcjdivDRiWuf4OYbGazz5GTE
+/SuWEnW+W9t7PRYfc5mxoHfpLiaMxAX03gwD7g1O1DDRkR/Uy7ir+6u/AoGAORUp
+qw+mIX7klfwLyIOEWCon34+XYsoOlLjA9raQjQOLEVlfZKwbHeTn82Swb2D61G7U
+upvFGJIb6I/+3p/8p6ZsbLXyGmjMgf+CeLyYzlh23JObO37kUpsobBJkOXIcKVtD
+U+rd1hT/b23Zrr7BBdyf4qKdkaw5E0w2w3TJ/mECgYAPNzz7Y42rn1N024MxRBd4
+AjaWRn4G1IslC3Xkcb2t5KALYQCEkb1q51wsSyHbQqXAvo+y7OyNdXByax51cDUm
+xnRep4AnNHlkFYYLQlrFaY4VeF6zOwqjp7JeyqkACb6lRg596/AQepc9av+uuIuN
+hWKE6tBe59J89Tn5oT9j2g==
+-----END PRIVATE KEY-----`;
+const CERT = `-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`;
+
+// Minimal implicit-FTPS server: completes the TLS handshake and greets with 220.
+class ImplicitTlsServer {
+    constructor() {
+        this.server = tls.createServer({ key: KEY, cert: CERT }, socket => {
+            socket.write("220 Welcome\r\n");
+        });
+    }
+    listen() {
+        return new Promise(resolve => this.server.listen(0, "127.0.0.1", resolve));
+    }
+    get address() {
+        return this.server.address();
+    }
+    close() {
+        this.server.close();
+    }
+}
+
+describe("Implicit TLS", () => {
+
+    let server, client;
+
+    beforeEach(async () => {
+        server = new ImplicitTlsServer();
+        await server.listen();
+        client = new Client(1000);
+    });
+
+    afterEach(() => {
+        client.close();
+        server.close();
+    });
+
+    // Regression for the Node.js v24.17.0 (CVE-2026-48934) change that binds a
+    // reusable TLS session to the host it was authenticated for. Data connections
+    // reuse the control connection's session, so the control host identity must be
+    // remembered on `tlsOptions`; otherwise data connections resume under a
+    // different identity and servers report the session as not resumed.
+    it("remembers the control host on tlsOptions so data connections can resume the session", async () => {
+        await client.connectImplicitTLS("127.0.0.1", server.address.port, { ca: CERT, rejectUnauthorized: true });
+        assert.strictEqual(client.ftp.tlsOptions.host, "127.0.0.1");
+    });
+
+    it("does not overwrite a host explicitly provided in secureOptions", async () => {
+        await client.connectImplicitTLS("127.0.0.1", server.address.port, { ca: CERT, rejectUnauthorized: true, host: "localhost" });
+        assert.strictEqual(client.ftp.tlsOptions.host, "localhost");
+    });
+});