diff --git a/src/DarkNet/models/DarknetServerOptions.ts b/src/DarkNet/models/DarknetServerOptions.ts
index ccdce54ca..2d4e4d984 100644
--- a/src/DarkNet/models/DarknetServerOptions.ts
+++ b/src/DarkNet/models/DarknetServerOptions.ts
@@ -18,6 +18,7 @@ import { hasFullDarknetAccess } from "../effects/effects";
 import { getFriendlyType, TypeAssertionError } from "../../utils/TypeAssertion";
 import { isIPAddress } from "../../Types/strings";
 import { roundToTwo } from "../../utils/helpers/roundToTwo";
+import { safelyReverseString } from "../../utils/StringHelperFunctions";
 
 export type PasswordResponse = {
   code: DarknetResponseCode;
@@ -158,11 +159,11 @@ const decorateName = (name: string): string => {
     const connector = connectors[Math.floor(Math.random() * connectors.length)];
 
     if (Math.random() < 0.3) {
-      updatedName = l33tifyName(name);
+      updatedName = l33tifyName(updatedName);
     }
 
     if (Math.random() < 0.05) {
-      updatedName = updatedName.split("").reverse().join("");
+      updatedName = safelyReverseString(updatedName);
     }
 
     if (Math.random() < 0.1) {
@@ -180,7 +181,11 @@ const decorateName = (name: string): string => {
     }
   } while (GetServer(updatedName) !== null);
 
-  return updatedName;
+  // Defensive coding. All operations above preserve well-formed UTF-16, so this is currently redundant. It's a
+  // safeguard to ensure the function never returns ill-formed UTF-16 if future changes introduce code unit–level
+  // manipulation.
+  // This normalization is lossy (lone surrogates -> U+FFFD).
+  return updatedName.toWellFormed();
 };
 
 const l33tifyName = (name: string): string => {
@@ -191,7 +196,11 @@ const l33tifyName = (name: string): string => {
     const replacement: string = l33t[char] ?? "";
     updatedName = updatedName.replaceAll(char, replacement);
   }
-  return updatedName;
+  // Defensive coding. All operations above preserve well-formed UTF-16, so this is currently redundant. It's a
+  // safeguard to ensure the function never returns ill-formed UTF-16 if future changes introduce code unit–level
+  // manipulation.
+  // This normalization is lossy (lone surrogates -> U+FFFD).
+  return updatedName.toWellFormed();
 };
 
 const getMaxRam = (difficulty: number): number => {
diff --git a/src/PersonObjects/Player/PlayerObject.ts b/src/PersonObjects/Player/PlayerObject.ts
index 02e8a968c..f3ac8abf7 100644
--- a/src/PersonObjects/Player/PlayerObject.ts
+++ b/src/PersonObjects/Player/PlayerObject.ts
@@ -212,6 +212,12 @@ export class PlayerObject extends Person implements IPlayer {
         delete player.jobs[loadedCompanyName as CompanyName];
       }
     }
+    // A bug created ill-formed UTF-16 darknet hostnames that caused the in-game editor to crash. Player.currentServer
+    // may point to one of these invalid hostnames. This code migrates the invalid hostnames and protects against
+    // similar issues in the future.
+    if (!player.currentServer.isWellFormed()) {
+      player.currentServer = player.currentServer.toWellFormed();
+    }
     return player;
   }
 }
diff --git a/src/Server/AllServers.ts b/src/Server/AllServers.ts
index 24720489e..a2116ce8d 100644
--- a/src/Server/AllServers.ts
+++ b/src/Server/AllServers.ts
@@ -148,6 +148,25 @@ export function loadAllServers(saveString: string): void {
     if (!(server instanceof Server) && !(server instanceof HacknetServer) && !(server instanceof DarknetServer)) {
       throw new Error(`Server ${serverName} is not an instance of Server or HacknetServer or DarknetServer.`);
     }
+    // Sanitize hostname
+    // A bug created ill-formed UTF-16 darknet hostnames that caused the in-game editor to crash. This code migrates
+    // those invalid hostnames and protects against similar issues in the future.
+    if (!server.hostname.isWellFormed()) {
+      server.hostname = server.hostname.toWellFormed();
+      for (const script of server.scripts.values()) {
+        script.server = server.hostname;
+      }
+      if (server.savedScripts) {
+        for (const script of server.savedScripts) {
+          script.server = server.hostname;
+        }
+      }
+    }
+    // Sanitize hostnames in server.serversOnNetwork
+    for (const [index, value] of server.serversOnNetwork.entries()) {
+      server.serversOnNetwork[index] = value.toWellFormed();
+    }
+
     AllServers.set(server.hostname, server);
     AllServers.set(server.ip, server);
   }
diff --git a/src/utils/ErrorHelper.ts b/src/utils/ErrorHelper.ts
index 63d9494f3..5d6a5729a 100644
--- a/src/utils/ErrorHelper.ts
+++ b/src/utils/ErrorHelper.ts
@@ -186,7 +186,9 @@ Copy your save here if possible
 \`\`\`
 `.trim();
 
-  const issueUrl = `${newIssueUrl}?title=${encodeURIComponent(title)}&body=${encodeURIComponent(body)}`;
+  const issueUrl = `${newIssueUrl}?title=${encodeURIComponent(title.toWellFormed())}&body=${encodeURIComponent(
+    body.toWellFormed(),
+  )}`;
 
   return {
     metadata,
diff --git a/src/utils/StringHelperFunctions.ts b/src/utils/StringHelperFunctions.ts
index 5991972e6..ee7496242 100644
--- a/src/utils/StringHelperFunctions.ts
+++ b/src/utils/StringHelperFunctions.ts
@@ -105,3 +105,18 @@ export function getKeyFromReactElements(a: string | React.JSX.Element, b: string
   const keyOfb = typeof b === "string" ? b : b.key ?? "";
   return keyOfA + keyOfb;
 }
+
+const graphemeSegmenter = new Intl.Segmenter(undefined, { granularity: "grapheme" });
+
+/**
+ * input.split("") operates on UTF-16 code units and can break surrogate pairs.
+ * For example, 'a🅱️b' is 'a\uD83C\uDD71\uFE0Fb'. A naive reverse yields 'b\uFE0F\uDD71\uD83Ca', which is ill-formed
+ * UTF-16 and not 'b🅱️a' as expected.
+ * Passing such a string to encodeURIComponent may throw a URIError (e.g. in Monaco editor code when processing model
+ * ids).
+ */
+export function safelyReverseString(input: string): string {
+  return Array.from(graphemeSegmenter.segment(input), (s) => s.segment)
+    .reverse()
+    .join("");
+}
diff --git a/test/jest/Darknet/Darknet.test.ts b/test/jest/Darknet/Darknet.test.ts
index 19f58f2c5..9fe4246f0 100644
--- a/test/jest/Darknet/Darknet.test.ts
+++ b/test/jest/Darknet/Darknet.test.ts
@@ -780,6 +780,7 @@ describe("mutateDarknet and webstorm", () => {
 function validatePath(hostname: string): void {
   expectWithMessage(isDirectoryPath(`${hostname}/`), true, `Invalid hostname: ${hostname}`);
   expectWithMessage(isFilePath(`${hostname}/data.txt`), true, `Invalid hostname: ${hostname}`);
+  expectWithMessage(hostname.isWellFormed(), true, `Malformed hostname: ${hostname}`);
 }
 
 describe("Darknet server name generator", () => {
diff --git a/test/jest/Migration/Migration.test.ts b/test/jest/Migration/Migration.test.ts
index 6d78f02c8..28e9a4876 100644
--- a/test/jest/Migration/Migration.test.ts
+++ b/test/jest/Migration/Migration.test.ts
@@ -6,6 +6,7 @@ import * as db from "../../../src/db";
 import * as FileUtils from "../../../src/utils/FileUtils";
 import type { SaveData } from "../../../src/types";
 import { calculateExp } from "../../../src/PersonObjects/formulas/skill";
+import { GetAllServers, GetServer } from "../../../src/Server/AllServers";
 
 async function loadGameFromSaveData(saveData: SaveData) {
   // Simulate loading the data in IndexedDB
@@ -132,4 +133,25 @@ describe("v3", () => {
       expect(mockedDownload).not.toHaveBeenCalled();
     });
   });
+
+  test("Malformed hostname", async () => {
+    const saveData = new Uint8Array(fs.readFileSync("test/jest/Migration/save-files/malformed-hostname.gz"));
+    await loadGameFromSaveData(saveData);
+    for (const server of GetAllServers(true)) {
+      expect(server.hostname.isWellFormed()).toBe(true);
+      for (const script of server.scripts.values()) {
+        expect(script.server).toStrictEqual(server.hostname);
+      }
+      if (server.savedScripts) {
+        for (const script of server.savedScripts) {
+          expect(script.server).toStrictEqual(server.hostname);
+        }
+      }
+      for (const hostname of server.serversOnNetwork) {
+        expect(hostname.isWellFormed()).toBe(true);
+        expect(GetServer(hostname)).not.toBeNull();
+      }
+    }
+    expect(() => Player.getCurrentServer()).not.toThrow();
+  });
 });
diff --git a/test/jest/Migration/save-files/malformed-hostname.gz b/test/jest/Migration/save-files/malformed-hostname.gz
new file mode 100644
index 000000000..a5decabb5
Binary files /dev/null and b/test/jest/Migration/save-files/malformed-hostname.gz differ