[alias_traversal] Minor improvements + respects path in the alias directive:

- alias /foo/bar/ -> HIGH severity
  - alias /foo/bar -> MEDIUM severity

gixy/directives/directive.py

@@ -131,3 +131,11 @@ class RootDirective(Directive):
     @property
     def variables(self):
         return [Variable(name='document_root', value=self.path, provider=self)]
+
+
+class AliasDirective(Directive):
+    nginx_name = 'alias'
+
+    def __init__(self, name, args):
+        super(AliasDirective, self).__init__(name, args)
+        self.path = args[0]

gixy/plugins/alias_traversal.py

@@ -11,7 +11,8 @@ class alias_traversal(Plugin):
     """
     summary = 'Path traversal via misconfigured alias.'
     severity = gixy.severity.HIGH
-    description = 'TODO'
+    description = 'Using alias in a prefixed location that doesn\'t ends with directory separator could lead to path ' \
+                  'traversal vulnerability. '
     help_url = 'https://github.com/yandex/gixy/blob/master/docs/en/plugins/aliastraversal.md'
     directives = ['alias']
 
@@ -19,8 +20,12 @@ class alias_traversal(Plugin):
         for location in directive.parents:
             if location.name != 'location':
                 continue
+
             if not location.modifier or location.modifier == '^~':
                 # We need non-strict prefixed locations
                 if not location.path.endswith('/'):
-                    self.add_issue(directive=[directive, location])
+                    self.add_issue(
+                        severity=gixy.severity.HIGH if directive.path.endswith('/') else gixy.severity.MEDIUM,
+                        directive=[directive, location]
+                    )
             break

tests/plugins/simply/alias_traversal/config.json

@@ -1,3 +1,3 @@
 {
-  "severity": "HIGH"
+  "severity": ["MEDIUM", "HIGH"]
 }

tests/plugins/simply/alias_traversal/not_slashed_alias.conf

@@ -0,0 +1,3 @@
+location /files {
+    alias /home;
+}

tests/plugins/simply/alias_traversal/not_slashed_alias_fp.conf

@@ -0,0 +1,3 @@
+location /files/ {
+    alias /home;
+}

tests/plugins/simply/alias_traversal/slashed_alias.conf

@@ -0,0 +1,3 @@
+location /files {
+    alias /home/;
+}

tests/plugins/simply/alias_traversal/slashed_alias_fp.conf

@@ -0,0 +1,3 @@
+location /files/ {
+    alias /home/;
+}