diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 6f4191443..8d7bd73a4 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -346,7 +346,7 @@ EOF;
         $classmapFile .= ");\n";
 
         if (!$suffix) {
-            if (!$config->get('autoloader-suffix') && is_readable($vendorPath.'/autoload.php')) {
+            if (!$config->get('autoloader-suffix') && Filesystem::isReadable($vendorPath.'/autoload.php')) {
                 $content = file_get_contents($vendorPath.'/autoload.php');
                 if (preg_match('{ComposerAutoloaderInit([^:\s]+)::}', $content, $match)) {
                     $suffix = $match[1];
@@ -1131,7 +1131,7 @@ INITIALIZER;
 
             foreach ($autoload[$type] as $namespace => $paths) {
                 foreach ((array) $paths as $path) {
-                    if (($type === 'files' || $type === 'classmap' || $type === 'exclude-from-classmap') && $package->getTargetDir() && !is_readable($installPath.'/'.$path)) {
+                    if (($type === 'files' || $type === 'classmap' || $type === 'exclude-from-classmap') && $package->getTargetDir() && !Filesystem::isReadable($installPath.'/'.$path)) {
                         // remove target-dir from file paths of the root package
                         if ($package === $rootPackage) {
                             $targetDir = str_replace('\\<dirsep\\>', '[\\\\/]', preg_quote(str_replace(array('/', '\\'), '<dirsep>', $package->getTargetDir())));
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index ec8c3de5b..abb0d5e9a 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -225,7 +225,7 @@ class ClassMapGenerator
         if (!$contents) {
             if (!file_exists($path)) {
                 $message = 'File at "%s" does not exist, check your classmap definitions';
-            } elseif (!is_readable($path)) {
+            } elseif (!Filesystem::isReadable($path)) {
                 $message = 'File at "%s" is not readable, check its permissions';
             } elseif ('' === trim(file_get_contents($path))) {
                 // The input file was really empty and thus contains no classes
diff --git a/src/Composer/Command/ConfigCommand.php b/src/Composer/Command/ConfigCommand.php
index b0f26deb2..232bb3742 100644
--- a/src/Composer/Command/ConfigCommand.php
+++ b/src/Composer/Command/ConfigCommand.php
@@ -12,6 +12,7 @@
 
 namespace Composer\Command;
 
+use Composer\Util\Filesystem;
 use Composer\Util\Platform;
 use Composer\Util\Silencer;
 use Symfony\Component\Console\Input\InputInterface;
@@ -411,7 +412,7 @@ EOT
             'secure-http' => array($booleanValidator, $booleanNormalizer),
             'cafile' => array(
                 function ($val) {
-                    return file_exists($val) && is_readable($val);
+                    return file_exists($val) && Filesystem::isReadable($val);
                 },
                 function ($val) {
                     return $val === 'null' ? null : $val;
@@ -419,7 +420,7 @@ EOT
             ),
             'capath' => array(
                 function ($val) {
-                    return is_dir($val) && is_readable($val);
+                    return is_dir($val) && Filesystem::isReadable($val);
                 },
                 function ($val) {
                     return $val === 'null' ? null : $val;
diff --git a/src/Composer/Command/InitCommand.php b/src/Composer/Command/InitCommand.php
index 6515c94db..6b514ebf8 100644
--- a/src/Composer/Command/InitCommand.php
+++ b/src/Composer/Command/InitCommand.php
@@ -796,7 +796,7 @@ EOT
         }
 
         $file = Factory::getComposerFile();
-        if (is_file($file) && is_readable($file) && is_array($composer = json_decode(file_get_contents($file), true))) {
+        if (is_file($file) && Filesystem::isReadable($file) && is_array($composer = json_decode(file_get_contents($file), true))) {
             if (!empty($composer['minimum-stability'])) {
                 return VersionParser::normalizeStability($composer['minimum-stability']);
             }
diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index ff98c484e..5dd9cde18 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -13,6 +13,7 @@
 namespace Composer\Command;
 
 use Composer\DependencyResolver\Request;
+use Composer\Util\Filesystem;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputOption;
@@ -119,9 +120,7 @@ EOT
 
             return 1;
         }
-        // check for readability by reading the file as is_readable can not be trusted on network-mounts
-        // see https://github.com/composer/composer/issues/8231 and https://bugs.php.net/bug.php?id=68926
-        if (!is_readable($this->file) && false === Silencer::call('file_get_contents', $this->file)) {
+        if (!Filesystem::isReadable($this->file)) {
             $io->writeError('<error>'.$this->file.' is not readable.</error>');
 
             return 1;
diff --git a/src/Composer/Command/SelfUpdateCommand.php b/src/Composer/Command/SelfUpdateCommand.php
index 54750d4ad..70e65d252 100644
--- a/src/Composer/Command/SelfUpdateCommand.php
+++ b/src/Composer/Command/SelfUpdateCommand.php
@@ -381,7 +381,7 @@ TAGSPUBKEY
         if (!is_file($oldFile)) {
             throw new FilesystemException('Composer rollback failed: "'.$oldFile.'" could not be found');
         }
-        if (!is_readable($oldFile)) {
+        if (!Filesystem::isReadable($oldFile)) {
             throw new FilesystemException('Composer rollback failed: "'.$oldFile.'" could not be read');
         }
 
@@ -582,7 +582,7 @@ EOT;
         @unlink($script);
 
         // see if the file was moved and is still accessible
-        if ($result = is_readable($localFilename) && (hash_file('sha256', $localFilename) === $checksum)) {
+        if ($result = Filesystem::isReadable($localFilename) && (hash_file('sha256', $localFilename) === $checksum)) {
             $io->writeError('<info>Operation succeeded.</info>');
             @unlink($newFilename);
         } else {
diff --git a/src/Composer/Command/ValidateCommand.php b/src/Composer/Command/ValidateCommand.php
index 128064f8e..0818c8c2f 100644
--- a/src/Composer/Command/ValidateCommand.php
+++ b/src/Composer/Command/ValidateCommand.php
@@ -17,6 +17,7 @@ use Composer\Package\Loader\ValidatingArrayLoader;
 use Composer\Plugin\CommandEvent;
 use Composer\Plugin\PluginEvents;
 use Composer\Util\ConfigValidator;
+use Composer\Util\Filesystem;
 use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
@@ -77,7 +78,7 @@ EOT
 
             return 3;
         }
-        if (!is_readable($file)) {
+        if (!Filesystem::isReadable($file)) {
             $io->writeError('<error>' . $file . ' is not readable.</error>');
 
             return 3;
diff --git a/src/Composer/Config/JsonConfigSource.php b/src/Composer/Config/JsonConfigSource.php
index 80cf51050..4be155782 100644
--- a/src/Composer/Config/JsonConfigSource.php
+++ b/src/Composer/Config/JsonConfigSource.php
@@ -15,6 +15,7 @@ namespace Composer\Config;
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
 use Composer\Json\JsonValidationException;
+use Composer\Util\Filesystem;
 use Composer\Util\Silencer;
 
 /**
@@ -217,7 +218,7 @@ class JsonConfigSource implements ConfigSourceInterface
                 throw new \RuntimeException(sprintf('The file "%s" is not writable.', $this->file->getPath()));
             }
 
-            if (!is_readable($this->file->getPath())) {
+            if (!Filesystem::isReadable($this->file->getPath())) {
                 throw new \RuntimeException(sprintf('The file "%s" is not readable.', $this->file->getPath()));
             }
 
diff --git a/src/Composer/Console/Application.php b/src/Composer/Console/Application.php
index 3dea8abe9..8b72eb31a 100644
--- a/src/Composer/Console/Application.php
+++ b/src/Composer/Console/Application.php
@@ -13,6 +13,7 @@
 namespace Composer\Console;
 
 use Composer\IO\NullIO;
+use Composer\Util\Filesystem;
 use Composer\Util\Platform;
 use Composer\Util\Silencer;
 use Symfony\Component\Console\Application as BaseApplication;
@@ -282,7 +283,7 @@ class Application extends BaseApplication
 
             // add non-standard scripts as own commands
             $file = Factory::getComposerFile();
-            if (is_file($file) && is_readable($file) && is_array($composer = json_decode(file_get_contents($file), true))) {
+            if (is_file($file) && Filesystem::isReadable($file) && is_array($composer = json_decode(file_get_contents($file), true))) {
                 if (isset($composer['scripts']) && is_array($composer['scripts'])) {
                     foreach ($composer['scripts'] as $script => $dummy) {
                         if (!defined('Composer\Script\ScriptEvents::'.str_replace('-', '_', strtoupper($script)))) {
diff --git a/src/Composer/Installer/LibraryInstaller.php b/src/Composer/Installer/LibraryInstaller.php
index fd1848f68..82a32520a 100644
--- a/src/Composer/Installer/LibraryInstaller.php
+++ b/src/Composer/Installer/LibraryInstaller.php
@@ -79,7 +79,7 @@ class LibraryInstaller implements InstallerInterface, BinaryPresenceInterface
 
         $installPath = $this->getInstallPath($package);
 
-        if (is_readable($installPath)) {
+        if (Filesystem::isReadable($installPath)) {
             return true;
         }
 
@@ -128,7 +128,7 @@ class LibraryInstaller implements InstallerInterface, BinaryPresenceInterface
         $downloadPath = $this->getInstallPath($package);
 
         // remove the binaries if it appears the package files are missing
-        if (!is_readable($downloadPath) && $repo->hasPackage($package)) {
+        if (!Filesystem::isReadable($downloadPath) && $repo->hasPackage($package)) {
             $this->binaryInstaller->removeBinaries($package);
         }
 
diff --git a/src/Composer/Util/Filesystem.php b/src/Composer/Util/Filesystem.php
index c1a122b11..8335052c7 100644
--- a/src/Composer/Util/Filesystem.php
+++ b/src/Composer/Util/Filesystem.php
@@ -600,6 +600,33 @@ class Filesystem
         return preg_replace('{^file://}i', '', $path);
     }
 
+    /**
+     * Cross-platform safe version of is_readable()
+     *
+     * This will also check for readability by reading the file as is_readable can not be trusted on network-mounts
+     * and \\wsl$ paths. See https://github.com/composer/composer/issues/8231 and https://bugs.php.net/bug.php?id=68926
+     *
+     * @param string $path
+     * @return bool
+     */
+    public static function isReadable($path)
+    {
+        if (is_readable($path)) {
+            return true;
+        }
+
+        if (is_file($path)) {
+            return false !== Silencer::call('file_get_contents', $path, false, null, 0, 1);
+        }
+
+        if (is_dir($path)) {
+            return false !== Silencer::call('opendir', $path);
+        }
+
+        // assume false otherwise
+        return false;
+    }
+
     protected function directorySize($directory)
     {
         $it = new RecursiveDirectoryIterator($directory, RecursiveDirectoryIterator::SKIP_DOTS);
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index e189c20ca..3545db105 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -211,11 +211,11 @@ final class StreamContextFactory
             }
         }
 
-        if (isset($defaults['ssl']['cafile']) && (!is_readable($defaults['ssl']['cafile']) || !CaBundle::validateCaFile($defaults['ssl']['cafile'], $logger))) {
+        if (isset($defaults['ssl']['cafile']) && (!Filesystem::isReadable($defaults['ssl']['cafile']) || !CaBundle::validateCaFile($defaults['ssl']['cafile'], $logger))) {
             throw new TransportException('The configured cafile was not valid or could not be read.');
         }
 
-        if (isset($defaults['ssl']['capath']) && (!is_dir($defaults['ssl']['capath']) || !is_readable($defaults['ssl']['capath']))) {
+        if (isset($defaults['ssl']['capath']) && (!is_dir($defaults['ssl']['capath']) || !Filesystem::isReadable($defaults['ssl']['capath']))) {
             throw new TransportException('The configured capath was not valid or could not be read.');
         }