diff --git a/eslint.config.js b/eslint.config.js
index 7984fb7..0582543 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -1,5 +1,6 @@
 import tseslint from '@typescript-eslint/eslint-plugin'
 import tsparser from '@typescript-eslint/parser'
+import security from 'eslint-plugin-security'
 
 export default [
   {
@@ -15,10 +16,24 @@ export default [
     },
     plugins: {
       '@typescript-eslint': tseslint,
+      security: security,
     },
     rules: {
       '@typescript-eslint/no-floating-promises': 'error',
       'no-console': ['warn', { allow: ['warn', 'error'] }],
+      // Security rules (from eslint-plugin-security)
+      'security/detect-buffer-noassert': 'warn',
+      'security/detect-child-process': 'warn',
+      'security/detect-eval-with-expression': 'error',
+      'security/detect-new-buffer': 'warn',
+      'security/detect-non-literal-regexp': 'warn',
+      'security/detect-non-literal-require': 'warn',
+      'security/detect-possible-timing-attacks': 'warn',
+      'security/detect-pseudoRandomBytes': 'warn',
+      'security/detect-unsafe-regex': 'error',
+      'security/detect-bidi-characters': 'error',
+      // detect-object-injection has too many false positives — skip
+      // detect-non-literal-fs-filename too noisy for server code — skip
     },
   },
   // Frontend game engine: fire-and-forget async (audio, animations) is intentional
diff --git a/package.json b/package.json
index dcfc5cf..22db46f 100644
--- a/package.json
+++ b/package.json
@@ -19,6 +19,7 @@
     "@typescript-eslint/parser": "^8.56.1",
     "concurrently": "^9.1.2",
     "eslint": "^10.0.3",
+    "eslint-plugin-security": "^4.0.0",
     "typescript": "^5.7.3",
     "vitest": "^3.1.1"
   }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 1fe0c9c..ff6fca3 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -27,6 +27,9 @@ importers:
       eslint:
         specifier: ^10.0.3
         version: 10.0.3(jiti@2.6.1)
+      eslint-plugin-security:
+        specifier: ^4.0.0
+        version: 4.0.0
       typescript:
         specifier: ^5.7.3
         version: 5.9.3
@@ -2162,6 +2165,10 @@ packages:
     resolution: {integrity: sha512-TtpcNJ3XAzx3Gq8sWRzJaVajRs0uVxA2YAkdb1jm2YkPz4G6egUFAyA3n5vtEIZefPk5Wa4UXbKuS5fKkJWdgA==}
     engines: {node: '>=10'}
 
+  eslint-plugin-security@4.0.0:
+    resolution: {integrity: sha512-tfuQT8K/Li1ZxhFzyD8wPIKtlzZxqBcPr9q0jFMQ77wWAbKBVEhaMPVQRTMTvCMUDhwBe5vPVqQPwAGk/ASfxQ==}
+    engines: {node: ^18.18.0 || ^20.9.0 || >=21.1.0}
+
   eslint-scope@9.1.2:
     resolution: {integrity: sha512-xS90H51cKw0jltxmvmHy2Iai1LIqrfbw57b79w/J7MfvDfkIkFZ+kj6zC3BjtUwh150HsSSdxXZcsuv72miDFQ==}
     engines: {node: ^20.19.0 || ^22.13.0 || >=24}
@@ -3051,6 +3058,10 @@ packages:
   regenerate@1.4.2:
     resolution: {integrity: sha512-zrceR/XhGYU/d/opr2EKO7aRHUeiBI8qjtfHqADTwZd6Szfy16la6kqD0MIUs5z5hx6AaKa+PixpPrR289+I0A==}
 
+  regexp-tree@0.1.27:
+    resolution: {integrity: sha512-iETxpjK6YoRWJG5o6hXLwvjYAoW+FEZn9os0PD/b6AP6xQwsa/Y7lCVgIixBbUPMfhu+i2LtdeAqVTgGlQarfA==}
+    hasBin: true
+
   regexp.prototype.flags@1.5.4:
     resolution: {integrity: sha512-dYqgNSZbDwkaJ2ceRd9ojCGjBq+mOm9LmtXnAnEGyHhN/5R7iDW2TRw3h+o/jCFxus3P2LfWIIiwowAjANm7IA==}
     engines: {node: '>= 0.4'}
@@ -3114,6 +3125,9 @@ packages:
     resolution: {integrity: sha512-x/+Cz4YrimQxQccJf5mKEbIa1NzeCRNI5Ecl/ekmlYaampdNLPalVyIcCZNNH3MvmqBugV5TMYZXv0ljslUlaw==}
     engines: {node: '>= 0.4'}
 
+  safe-regex@2.1.1:
+    resolution: {integrity: sha512-rx+x8AMzKb5Q5lQ95Zoi6ZbJqwCLkqi3XuJXp5P3rT8OEc6sZCJG5AE5dU3lsgRr/F4Bs31jSlVN+j5KrsGu9A==}
+
   saxes@6.0.0:
     resolution: {integrity: sha512-xAg7SOnEhrm5zI3puOOKyy1OMcMlIJZYNJY7xLBwSze0UjhPLnWfj2GF2EpT0jmzaJKIWKHLsaSSajf35bcYnA==}
     engines: {node: '>=v12.22.7'}
@@ -5791,6 +5805,10 @@ snapshots:
 
   escape-string-regexp@4.0.0: {}
 
+  eslint-plugin-security@4.0.0:
+    dependencies:
+      safe-regex: 2.1.1
+
   eslint-scope@9.1.2:
     dependencies:
       '@types/esrecurse': 4.3.1
@@ -6681,6 +6699,8 @@ snapshots:
 
   regenerate@1.4.2: {}
 
+  regexp-tree@0.1.27: {}
+
   regexp.prototype.flags@1.5.4:
     dependencies:
       call-bind: 1.0.8
@@ -6786,6 +6806,10 @@ snapshots:
       es-errors: 1.3.0
       is-regex: 1.2.1
 
+  safe-regex@2.1.1:
+    dependencies:
+      regexp-tree: 0.1.27
+
   saxes@6.0.0:
     dependencies:
       xmlchars: 2.2.0
diff --git a/server/src/engine/answers.ts b/server/src/engine/answers.ts
index e86fad0..6c331aa 100644
--- a/server/src/engine/answers.ts
+++ b/server/src/engine/answers.ts
@@ -155,6 +155,7 @@ export function checkAnswer(response: string | null, acceptedAnswers: string[]):
     if (accNum !== null) {
       const numStr = String(accNum)
       // Only match if the number appears as a whole token, not as a substring of a larger number
+      // eslint-disable-next-line security/detect-non-literal-regexp -- numStr is a parsed number, escaped
       const numRegex = new RegExp(`(?<![\\d])${numStr.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}(?![\\d])`)
       if (numRegex.test(normResponse)) return 1.0
       // Check number words in response