diff -r 7ed567ad8b4c Lib/http/cookies.py
--- a/Lib/http/cookies.py	Tue Mar 31 22:03:59 2015 +0200
+++ b/Lib/http/cookies.py	Tue Mar 31 16:58:33 2015 -0700
@@ -455,12 +455,13 @@
 # result, the parsing rules here are less strict.
 #
 
-_LegalCharsPatt  = r"[\w\d!#%&'~_`><@,:/\$\*\+\-\.\^\|\)\(\?\}\{\=]"
+_LegalCharsPatt  = r"\w\d!#%&'~_`><@,:/\$\*\+\-\.\^\|\)\(\?\}\{\="
+_LegalValuesPatt = _LegalCharsPatt + '\[\]'
 _CookiePattern = re.compile(r"""
     (?x)                           # This is a verbose pattern
     \s*                            # Optional whitespace at start of cookie
     (?P<key>                       # Start of group 'key'
-    """ + _LegalCharsPatt + r"""+?   # Any word of at least one letter
+    [""" + _LegalCharsPatt + r"""]+?   # Any word of at least one letter
     )                              # End of group 'key'
     (                              # Optional group: there may not be a value.
     \s*=\s*                          # Equal Sign
@@ -469,7 +470,7 @@
     |                                  # or
     \w{3},\s[\w\d\s-]{9,11}\s[\d:]{8}\sGMT  # Special case for "expires" attr
     |                                  # or
-    """ + _LegalCharsPatt + r"""*      # Any word or empty string
+    [""" + _LegalValuesPatt + r"""]*     # Any word or empty string
     )                                # End of group 'val'
     )?                             # End of optional value group
     \s*                            # Any number of spaces.
diff -r 7ed567ad8b4c Lib/test/test_http_cookies.py
--- a/Lib/test/test_http_cookies.py	Tue Mar 31 22:03:59 2015 +0200
+++ b/Lib/test/test_http_cookies.py	Tue Mar 31 16:58:33 2015 -0700
@@ -44,6 +44,19 @@
              'repr': "<SimpleCookie: key:term='value:term'>",
              'output': 'Set-Cookie: key:term=value:term'},
 
+            # issue22931 - Adding '[' and ']' as valid characters in cookie
+            # values as defined in RFC 6265
+            {
+                'data': 'a=b; c=[; d=r; f=h',
+                'dict': {'a':'b', 'c':'[', 'd':'r', 'f':'h'},
+                'repr': "<SimpleCookie: a='b' c='[' d='r' f='h'>",
+                'output': '\n'.join((
+                    'Set-Cookie: a=b',
+                    'Set-Cookie: c=[',
+                    'Set-Cookie: d=r',
+                    'Set-Cookie: f=h'
+                ))
+            }
         ]
 
         for case in cases: