diff --git a/_pr_meta.json b/_pr_meta.json
new file mode 100644
index 00000000..d11745dc
--- /dev/null
+++ b/_pr_meta.json
@@ -0,0 +1,9 @@
+{
+  "repo": "Eyevinn/intercom-frontend",
+  "number": 671,
+  "base": "main",
+  "head": "fix/issue-627",
+  "fork": "VedantMadane/Eyevinn-intercom-frontend",
+  "title": "fix: Validate companion host before WebSocket URL construction",
+  "url": "https://github.com/Eyevinn/intercom-frontend/pull/671"
+}
\ No newline at end of file
diff --git a/src/utils/call-url.test.ts b/src/utils/call-url.test.ts
index 04932d45..4d27ab3a 100644
--- a/src/utils/call-url.test.ts
+++ b/src/utils/call-url.test.ts
@@ -4,6 +4,7 @@ import {
   encodeCallsParam,
   decodeCallsParam,
   parseCompanionParam,
+  isValidCompanionHost,
 } from "./call-url";
 
 describe("buildCallsUrl", () => {
@@ -88,6 +89,26 @@ describe("buildCallsUrl round-trip", () => {
   });
 });
 
+describe("isValidCompanionHost", () => {
+  // Regression: locks in the SSRF-hardening behaviour so future edits to the
+  // host[:port] validator cannot silently reintroduce scheme/path/userinfo or
+  // out-of-range port acceptance.
+  it.each([
+    ["localhost", true],
+    ["localhost:8080", true],
+    ["[::1]", true],
+    ["[::1]:443", true],
+    ["", false],
+    ["http://evil.com", false],
+    ["host/path", false],
+    ["host:99999", false], // port out of range
+    ["host:0", false], // port zero
+    ["a".repeat(254), false], // over-length host (> 253)
+  ])("%s -> %s", (host, expected) => {
+    expect(isValidCompanionHost(host)).toBe(expected);
+  });
+});
+
 describe("buildCallsUrl — companion URL", () => {
   it("appends companion param by stripping the ws:// prefix", () => {
     const url = buildCallsUrl(
@@ -115,6 +136,25 @@ describe("buildCallsUrl — companion URL", () => {
       "/calls?lines=p1:l1"
     );
   });
+
+  it("omits the companion param entirely for an invalid host", () => {
+    // Regression: an SSRF-shaped companion must never leak into the URL.
+    const url = buildCallsUrl(
+      [{ productionId: "p1", lineId: "l1" }],
+      "http://evil.com/path"
+    );
+    expect(url).toBe("/calls?lines=p1:l1");
+    expect(url).not.toContain("companion=");
+  });
+
+  it("includes the companion param for a valid host", () => {
+    const url = buildCallsUrl(
+      [{ productionId: "p1", lineId: "l1" }],
+      "ws://companion.example:8080"
+    );
+    expect(url).toBe("/calls?lines=p1:l1&companion=companion.example:8080");
+    expect(url).toContain("companion=companion.example:8080");
+  });
 });
 
 describe("parseCompanionParam", () => {
@@ -130,3 +170,41 @@ describe("parseCompanionParam", () => {
     expect(parseCompanionParam("example.com")).toBe("ws://example.com");
   });
 });
+
+describe("parseCompanionParam rejects unsafe hosts", () => {
+  it.each([
+    "attacker.com/malicious",
+    "user@evil.com",
+    "//evil.com",
+    "host:99999",
+    "host:0",
+    "evil.com/path",
+    " user.com ",
+  ])("rejects %s", (raw) => {
+    expect(parseCompanionParam(raw)).toBeUndefined();
+  });
+
+  it("accepts a bare host and host:port", () => {
+    expect(parseCompanionParam("companion.example")).toBe(
+      "ws://companion.example"
+    );
+    expect(parseCompanionParam("companion.example:8080")).toBe(
+      "ws://companion.example:8080"
+    );
+  });
+
+  it("strips accidental ws scheme then validates", () => {
+    expect(parseCompanionParam("ws://companion.example:8080")).toBe(
+      "ws://companion.example:8080"
+    );
+    expect(parseCompanionParam("ws://user@evil.com")).toBeUndefined();
+  });
+
+  it("strips an accidental wss scheme and re-wraps a valid host as ws://", () => {
+    // Real behaviour: the scheme is normalised away and the returned URL is
+    // always ws:// regardless of the incoming ws:// or wss:// prefix.
+    expect(parseCompanionParam("wss://companion.example:8080")).toBe(
+      "ws://companion.example:8080"
+    );
+  });
+});
diff --git a/src/utils/call-url.ts b/src/utils/call-url.ts
index 268087ff..6ab98ff2 100644
--- a/src/utils/call-url.ts
+++ b/src/utils/call-url.ts
@@ -30,19 +30,40 @@ export function decodeCallsParam(param: string | null): CallRef[] {
   }, []);
 }
 
+/** Host[:port] only — reject schemes, paths, userinfo, and other SSRF-friendly shapes. */
+const COMPANION_HOST_RE =
+  /^(?:(?:\[[0-9a-fA-F:.]+\]|[A-Za-z0-9.-]+))(?::\d{1,5})?$/;
+
+export function isValidCompanionHost(hostPort: string): boolean {
+  if (!hostPort || hostPort.length > 253) return false;
+  if (!COMPANION_HOST_RE.test(hostPort)) return false;
+  // Reject port 0 and oversized ports.
+  const colon = hostPort.lastIndexOf(":");
+  if (colon > 0 && !hostPort.endsWith("]")) {
+    const port = Number(hostPort.slice(colon + 1));
+    if (!Number.isInteger(port) || port < 1 || port > 65535) return false;
+  }
+  return true;
+}
+
 export function buildCallsUrl(calls: CallRef[], companionUrl?: string): string {
   const base =
     calls.length === 0 ? "/calls" : `/calls?lines=${encodeCallsParam(calls)}`;
   let url = base;
   if (companionUrl) {
-    const hostPort = companionUrl.replace(/^wss?:\/\//, "");
-    const sep = url.includes("?") ? "&" : "?";
-    url = `${url}${sep}companion=${hostPort}`;
+    const hostPort = companionUrl.replace(/^wss?:\/\//i, "");
+    if (isValidCompanionHost(hostPort)) {
+      const sep = url.includes("?") ? "&" : "?";
+      url = `${url}${sep}companion=${hostPort}`;
+    }
   }
   return url;
 }
 
 export function parseCompanionParam(param: string | null): string | undefined {
   if (!param) return undefined;
-  return `ws://${param}`;
+  // Strip accidental scheme if present, then validate host[:port] only.
+  const hostPort = param.replace(/^wss?:\/\//i, "");
+  if (!isValidCompanionHost(hostPort)) return undefined;
+  return `ws://${hostPort}`;
 }