feat: add 'Last only' defang mode to Defang IP Addresses

Adds an opt-in "Last only" boolean argument (default false to preserve
existing behaviour) to the Defang IP Addresses operation. When enabled,
only the final separator of each matched IP is replaced:

- IPv4: 1.2.3.4 -> 1.2.3[.]4 (instead of 1[.]2[.]3[.]4)
- IPv6: 2001:0db8::1 -> 2001:0db8::[:]1

This matches the common SOC-tool default (e.g. Splunk) where the
defanged form stays visually close to the original while still
rendering the address invalid.

src/core/operations/DefangIPAddresses.mjs

@@ -20,11 +20,17 @@ class DefangIPAddresses extends Operation {
 
         this.name = "Defang IP Addresses";
         this.module = "Default";
-        this.description = "Takes a IPv4 or IPv6 address and 'Defangs' it, meaning the IP becomes invalid, removing the risk of accidentally utilising it as an IP address.";
+        this.description = "Takes a IPv4 or IPv6 address and 'Defangs' it, meaning the IP becomes invalid, removing the risk of accidentally utilising it as an IP address.<br><br>When 'Last only' is enabled, only the final separator of each IP is replaced (e.g. <code>1.2.3.4</code> becomes <code>1.2.3[.]4</code>), keeping the address visually closer to its original form while still rendering it invalid.";
         this.infoURL = "https://isc.sans.edu/forums/diary/Defang+all+the+things/22744/";
         this.inputType = "string";
         this.outputType = "string";
-        this.args = [];
+        this.args = [
+            {
+                name: "Last only",
+                type: "boolean",
+                value: false
+            }
+        ];
         this.checks = [
             {
                 pattern: "^\\s*(([0-9]{1,3}\\.){3}[0-9]{1,3}|([0-9a-f]{4}:){7}[0-9a-f]{4})\\s*$",
@@ -44,12 +50,14 @@ class DefangIPAddresses extends Operation {
      * @returns {string}
      */
     run(input, args) {
+        const [lastOnly] = args;
+
         input = input.replace(IPV4_REGEX, x => {
-            return x.replace(/\./g, "[.]");
+            return defangSeparators(x, ".", "[.]", lastOnly);
         });
 
         input = input.replace(IPV6_REGEX, x => {
-            return x.replace(/:/g, "[:]");
+            return defangSeparators(x, ":", "[:]", lastOnly);
         });
 
         return input;
@@ -59,6 +67,26 @@ class DefangIPAddresses extends Operation {
 export default DefangIPAddresses;
 
 
+/**
+ * Replaces a separator character with a defanged token.
+ * If lastOnly is true, only the final occurrence is replaced.
+ *
+ * @param {string} match
+ * @param {string} sep
+ * @param {string} token
+ * @param {boolean} lastOnly
+ * @returns {string}
+ */
+function defangSeparators(match, sep, token, lastOnly) {
+    if (!lastOnly) {
+        return match.split(sep).join(token);
+    }
+    const idx = match.lastIndexOf(sep);
+    if (idx === -1) return match;
+    return match.slice(0, idx) + token + match.slice(idx + sep.length);
+}
+
+
 /**
  * IPV4 regular expression
  */

tests/operations/tests/DefangIP.mjs

@@ -39,5 +39,45 @@ TestRegister.addTests([
                 args: [],
             },
         ],
+    }, {
+        name: "Defang IP: Last only — IPV4",
+        input: "192.168.1.1",
+        expectedOutput: "192.168.1[.]1",
+        recipeConfig: [
+            {
+                op: "Defang IP Addresses",
+                args: [true],
+            },
+        ],
+    }, {
+        name: "Defang IP: Last only — IPV6",
+        input: "2001:0db8:85a3:0000:0000:8a2e:0370:7343",
+        expectedOutput: "2001:0db8:85a3:0000:0000:8a2e:0370[:]7343",
+        recipeConfig: [
+            {
+                op: "Defang IP Addresses",
+                args: [true],
+            },
+        ],
+    }, {
+        name: "Defang IP: Last only — IPV6 shorthand",
+        input: "2001:db8:3c4d:15::1a2f:1a2b",
+        expectedOutput: "2001:db8:3c4d:15::1a2f[:]1a2b",
+        recipeConfig: [
+            {
+                op: "Defang IP Addresses",
+                args: [true],
+            },
+        ],
+    }, {
+        name: "Defang IP: Last only — multiple IPs in text",
+        input: "From 10.0.0.1 to 192.168.1.254",
+        expectedOutput: "From 10.0.0[.]1 to 192.168.1[.]254",
+        recipeConfig: [
+            {
+                op: "Defang IP Addresses",
+                args: [true],
+            },
+        ],
     },
 ]);