diff --git a/lib/config.js b/lib/config.js
index 7b960f8998a4..1f9242f41f00 100644
--- a/lib/config.js
+++ b/lib/config.js
@@ -118,13 +118,13 @@ class Config {
         };
 
         this.cliConfig = {};
-        Object.keys(cliConfigOptions).forEach(function(configKey) {
+        Object.keys(cliConfigOptions).forEach(configKey => {
             const value = cliConfigOptions[configKey];
 
             if (value) {
                 this.cliConfig[configKey] = value;
             }
-        }, this);
+        });
     }
 
     /**
@@ -290,7 +290,7 @@ class Config {
                 return;
             }
 
-            const relativePath = (filePath || directory).substr(config.baseDirectory.length + 1);
+            const relativePath = path.relative(config.baseDirectory, filePath || directory);
 
             overrides.forEach((override, i) => {
                 if (ConfigOps.pathMatchesGlobs(relativePath, override.files)) {
diff --git a/lib/config/config-file.js b/lib/config/config-file.js
index 0dcd6ebfb2a1..14cf0639f716 100644
--- a/lib/config/config-file.js
+++ b/lib/config/config-file.js
@@ -567,13 +567,12 @@ function loadObject(configObject) {
  */
 function loadCached(filePath) {
     const cachedConfig = configCache.getConfig(filePath);
-    let config = {};
 
     if (cachedConfig) {
         return cachedConfig;
     }
 
-    config = load(filePath);
+    const config = load(filePath);
 
     if (config) {
         config.filePath = filePath;
diff --git a/lib/config/config-ops.js b/lib/config/config-ops.js
index f8f04e2dd184..5c4b72eff0f1 100644
--- a/lib/config/config-ops.js
+++ b/lib/config/config-ops.js
@@ -11,7 +11,8 @@
 
 const Environments = require("./environments"),
     configCache = require("./config-cache"),
-    minimatch = require("minimatch");
+    minimatch = require("minimatch"),
+    path = require("path");
 
 const debug = require("debug")("eslint:config-ops");
 
@@ -289,12 +290,13 @@ module.exports = {
             nearestCacheIndex = vector.length - 1;
 
         // Check the merged vector config cache to try to find a merged config for the current config or a parent
-        for (; nearestCacheIndex >= 0; nearestCacheIndex--) {
+        while (nearestCacheIndex >= 0) {
             config = configCache.getMergedVectorConfig(subvector);
             if (config) {
                 break;
             }
             subvector.pop();
+            nearestCacheIndex--;
         }
 
         if (config) {
@@ -349,7 +351,12 @@ module.exports = {
      * @returns {boolean} True if all the supplied patterns match the file path, false otherwise
      */
     pathMatchesGlobs(filePath, patterns) {
-        patterns = [].concat(patterns);
-        return patterns.every(pattern => minimatch(filePath, pattern, { matchBase: true }));
+        const validPatterns = [].concat(patterns).filter(
+            pattern => !path.isAbsolute(pattern) && !pattern.includes("..")
+        );
+
+        return validPatterns.length > 0 && validPatterns.every(
+          pattern => minimatch(filePath, pattern, { matchBase: true })
+        );
     }
 };
diff --git a/tests/lib/config.js b/tests/lib/config.js
index 0dcd22e8631f..69c3d1017d5e 100644
--- a/tests/lib/config.js
+++ b/tests/lib/config.js
@@ -1157,6 +1157,32 @@ describe("Config", () => {
                 assertConfigsEqual(actual, expected);
             });
 
+            it("should not merge override config when the pattern traverses up the directory tree", () => {
+                const targetPath = getFakeFixturePath("overrides", "bar.js");
+                const parentPath = "overrides/../**/*.js";
+
+                const config = new Config({
+                    cwd: process.cwd(),
+                    baseConfig: {
+                        overrides: [{
+                            files: parentPath,
+                            rules: {
+                                quotes: [2, "single"]
+                            }
+                        }],
+                        useEslintrc: false
+                    }
+                });
+                const expected = {
+                    rules: {
+                        quotes: [2, "double"]
+                    }
+                };
+                const actual = config.getConfig(targetPath);
+
+                assertConfigsEqual(actual, expected);
+            });
+
             it("should merge all local configs (override and non-override) before non-local configs", () => {
                 const config = new Config({ cwd: process.cwd() });
                 const targetPath = getFakeFixturePath("overrides", "two", "child-two.js");