diff --git a/.changeset/tidy-host-headers.md b/.changeset/tidy-host-headers.md
new file mode 100644
index 0000000000..0f3562e27e
--- /dev/null
+++ b/.changeset/tidy-host-headers.md
@@ -0,0 +1,5 @@
+---
+"webpack-dev-server": patch
+---
+
+Validate Host and HTTP/2 authority headers independently of Origin protocol exceptions, including when `allowedHosts` is `"all"`. Handle malformed open-editor URLs with a controlled response and parse their query without relying on the Host header.
diff --git a/lib/Server.js b/lib/Server.js
index db9e880ab7..486acf79d7 100644
--- a/lib/Server.js
+++ b/lib/Server.js
@@ -2230,7 +2230,17 @@ class Server {
           return;
         }
 
-        const resolveUrl = new URL(req.url, `http://${req.headers.host}`);
+        let resolveUrl;
+
+        try {
+          // Only the query is needed; parsing must not depend on the Host header.
+          resolveUrl = new URL(req.url, "http://localhost");
+        } catch {
+          res.statusCode = 400;
+          res.end("Invalid URL");
+          return;
+        }
+
         const params = new URLSearchParams(resolveUrl.search);
         const fileName = params.get("fileName");
 
@@ -3321,7 +3331,9 @@ class Server {
    * @returns {boolean} true when host is valid, otherwise false
    */
   isValidHost(headers, headerToCheck, validateHost = true) {
-    if (this.options.allowedHosts === "all") {
+    const isOrigin = headerToCheck === "origin";
+
+    if (isOrigin && this.options.allowedHosts === "all") {
       return true;
     }
 
@@ -3333,14 +3345,24 @@ class Server {
       return false;
     }
 
-    if (DEFAULT_ALLOWED_PROTOCOLS.test(header)) {
+    if (isOrigin && DEFAULT_ALLOWED_PROTOCOLS.test(header)) {
       return true;
     }
 
+    // Host and :authority contain a hostname and optional port, never a URL.
+    if (!isOrigin && /[/\\?#@\s]/.test(header)) {
+      return false;
+    }
+
     // use the node url-parser to retrieve the hostname from the host-header.
     let hostname;
 
     try {
+      // Validate authority syntax before the legacy parser, which accepts invalid ports.
+      if (!isOrigin && !new URL(`http://${header}`).hostname) {
+        return false;
+      }
+
       // if header doesn't have scheme, add // for parsing.
       // TODO resolve me in the next major release
       // eslint-disable-next-line n/no-deprecated-api
@@ -3357,7 +3379,7 @@ class Server {
       return false;
     }
 
-    if (this.isHostAllowed(hostname)) {
+    if (this.options.allowedHosts === "all" || this.isHostAllowed(hostname)) {
       return true;
     }
 
@@ -3419,17 +3441,19 @@ class Server {
       return this.options.allowedHosts === "all";
     }
 
-    if (DEFAULT_ALLOWED_PROTOCOLS.test(hostHeader)) {
-      return true;
-    }
+    let host;
 
-    // eslint-disable-next-line n/no-deprecated-api
-    const host = url.parse(
-      // if hostHeader doesn't have scheme, add // for parsing.
-      /^(.+:)?\/\//.test(hostHeader) ? hostHeader : `//${hostHeader}`,
-      false,
-      true,
-    ).hostname;
+    try {
+      // eslint-disable-next-line n/no-deprecated-api
+      ({ hostname: host } = url.parse(
+        // if hostHeader doesn't have scheme, add // for parsing.
+        /^(.+:)?\/\//.test(hostHeader) ? hostHeader : `//${hostHeader}`,
+        false,
+        true,
+      ));
+    } catch {
+      return false;
+    }
 
     if (host === null) {
       return false;
diff --git a/test/ports-map.js b/test/ports-map.js
index ecd1fb24a8..bf4cc155a8 100644
--- a/test/ports-map.js
+++ b/test/ports-map.js
@@ -83,6 +83,7 @@ const listOfTests = {
   app: 1,
   "cross-origin-request": 2,
   "proxy-web-socket-origin": 2,
+  "host-header-validation": 1,
 };
 
 let startPort = 8089;
diff --git a/test/server/host-header-validation.test.js b/test/server/host-header-validation.test.js
new file mode 100644
index 0000000000..5eddbecd81
--- /dev/null
+++ b/test/server/host-header-validation.test.js
@@ -0,0 +1,184 @@
+"use strict";
+
+const launchEditor = require("launch-editor");
+const request = require("supertest");
+const webpack = require("webpack");
+const Server = require("../../lib/Server");
+const config = require("../fixtures/simple-config/webpack.config");
+const port = require("../ports-map")["host-header-validation"];
+
+jest.mock("launch-editor", () => jest.fn());
+
+const allowedHostsOptions = ["auto", ["trusted.example"], "all"];
+const invalidHosts = [
+  "file:invalid",
+  "chrome-extension:invalid",
+  "moz-extension:invalid",
+  "localhost:invalid",
+  "localhost:65536",
+  "http://localhost",
+  "//localhost",
+  "user@localhost",
+  "localhost/path",
+  "localhost\\path",
+  "localhost?query",
+  "localhost#fragment",
+  " localhost",
+  "localhost ",
+];
+
+describe("Host header validation", () => {
+  for (const allowedHosts of allowedHostsOptions) {
+    describe(`with allowedHosts ${JSON.stringify(allowedHosts)}`, () => {
+      const server = new Server({ allowedHosts }, webpack(config));
+
+      for (const headerName of ["host", ":authority"]) {
+        for (const value of invalidHosts) {
+          it(`should reject ${headerName} ${JSON.stringify(value)}`, () => {
+            expect(
+              server.isValidHost({ [headerName]: value }, headerName),
+            ).toBe(false);
+          });
+        }
+
+        for (const value of [
+          "localhost",
+          "localhost:8080",
+          "127.0.0.1:8080",
+          "[::1]:8080",
+        ]) {
+          it(`should accept ${headerName} ${value}`, () => {
+            expect(
+              server.isValidHost({ [headerName]: value }, headerName),
+            ).toBe(true);
+          });
+        }
+      }
+    });
+  }
+
+  it("should check hosts named file or chrome-extension against allowedHosts", () => {
+    for (const host of ["file", "chrome-extension"]) {
+      expect(
+        new Server({ allowedHosts: "auto" }, webpack(config)).isValidHost(
+          { host: `${host}:80` },
+          "host",
+        ),
+      ).toBe(false);
+      expect(
+        new Server({ allowedHosts: [host] }, webpack(config)).isValidHost(
+          { host: `${host}:80` },
+          "host",
+        ),
+      ).toBe(true);
+    }
+  });
+
+  it("should not treat a Host with an Origin protocol as same-origin", () => {
+    const server = new Server({ allowedHosts: "auto" }, webpack(config));
+
+    for (const host of [
+      "file:invalid",
+      "chrome-extension:invalid",
+      "file:80",
+    ]) {
+      expect(server.isSameOrigin({ host, origin: "http://example.com" })).toBe(
+        false,
+      );
+    }
+  });
+});
+
+describe("Origin header validation", () => {
+  for (const allowedHosts of allowedHostsOptions) {
+    describe(`with allowedHosts ${JSON.stringify(allowedHosts)}`, () => {
+      const server = new Server({ allowedHosts }, webpack(config));
+
+      for (const origin of [
+        "file:///index.html",
+        "chrome-extension://extension-id",
+        "moz-extension://extension-id",
+        "http://localhost:8080",
+        "http://127.0.0.1:8080",
+        "http://[::1]:8080",
+      ]) {
+        it(`should still accept Origin ${origin}`, () => {
+          expect(server.isValidHost({ origin }, "origin")).toBe(true);
+        });
+      }
+
+      for (const origin of [undefined, "null", "http://untrusted.example"]) {
+        it(`should accept Origin ${origin} only when allowedHosts is all`, () => {
+          expect(server.isValidHost({ origin }, "origin")).toBe(
+            allowedHosts === "all",
+          );
+        });
+      }
+
+      it("should honor the configured allowed hostname for Origin", () => {
+        expect(
+          server.isValidHost(
+            { origin: "http://trusted.example:8080" },
+            "origin",
+          ),
+        ).toBe(allowedHosts !== "auto");
+      });
+    });
+  }
+});
+
+describe("Open editor URL handling", () => {
+  beforeEach(() => {
+    launchEditor.mockClear();
+  });
+
+  for (const allowedHosts of allowedHostsOptions) {
+    describe(`with allowedHosts ${JSON.stringify(allowedHosts)}`, () => {
+      const server = new Server({ allowedHosts, port }, webpack(config));
+
+      beforeAll(async () => {
+        await server.start();
+      });
+
+      afterAll(async () => {
+        await server.stop();
+      });
+
+      for (const host of ["file:invalid", "chrome-extension:invalid"]) {
+        for (const route of ["/webpack-dev-server/open-editor", "/main.js"]) {
+          it(`should reject Host ${host} on ${route} without exposing a stack trace`, async () => {
+            const response = await request(server.app)
+              .get(route)
+              .set("Host", host);
+
+            expect(response.status).toBe(403);
+            expect(response.text).toBe("Invalid Host header");
+            expect(launchEditor).not.toHaveBeenCalled();
+          });
+        }
+      }
+
+      it("should reject malformed request URLs without exposing a stack trace", async () => {
+        const response = await request(server.app)
+          .get("/webpack-dev-server/open-editor///[")
+          .set("Host", "localhost");
+
+        expect(response.status).toBe(400);
+        expect(response.text).toBe("Invalid URL");
+        expect(launchEditor).not.toHaveBeenCalled();
+      });
+
+      it("should still pass the requested file name to the editor", async () => {
+        const fileName = "./src/file with spaces.js:3:7";
+        const response = await request(server.app)
+          .get("/webpack-dev-server/open-editor")
+          .query({ fileName })
+          .set("Host", "localhost");
+
+        expect(response.status).toBe(200);
+        expect(launchEditor).toHaveBeenCalledTimes(1);
+        expect(launchEditor).toHaveBeenCalledWith(fileName);
+      });
+    });
+  }
+});