From 5ea7ee4e955d96177e461b0a1f2c2be04df12ea8 Mon Sep 17 00:00:00 2001
From: Mark Sapiro <mark@msapiro.net>
Date: Mon, 18 Oct 2021 16:56:42 -0700
Subject: Fixes for CVEs 2021-42096 and 2021-42097.

---
 Mailman/CSRFcheck.py       | 22 +++++++++++++++++++---
 Mailman/Cgi/options.py     | 25 ++++++++++++-------------
 Mailman/SecurityManager.py |  1 +
 3 files changed, 32 insertions(+), 16 deletions(-)

(limited to 'Mailman')

diff --git a/Mailman/CSRFcheck.py b/Mailman/CSRFcheck.py
index a1e78d98..24e3e11b 100644
--- a/Mailman/CSRFcheck.py
+++ b/Mailman/CSRFcheck.py
@@ -18,11 +18,13 @@
 """ Cross-Site Request Forgery checker """
 
 import time
+import urllib
 import marshal
 import binascii
 
 from Mailman import mm_cfg
-from Mailman.Utils import sha_new
+from Mailman.Logging.Syslog import syslog
+from Mailman.Utils import UnobscureEmail, sha_new
 
 keydict = {
     'user':      mm_cfg.AuthUser,
@@ -37,6 +39,10 @@ keydict = {
 def csrf_token(mlist, contexts, user=None):
     """ create token by mailman cookie generation algorithm """
 
+    if user:
+        # Unmunge a munged email address.
+        user = UnobscureEmail(urllib.unquote(user))
+        
     for context in contexts:
         key, secret = mlist.AuthContextInfo(context, user)
         if key:
@@ -49,9 +55,8 @@ def csrf_token(mlist, contexts, user=None):
     token = binascii.hexlify(marshal.dumps((issued, keymac)))
     return token
 
-def csrf_check(mlist, token):
+def csrf_check(mlist, token, options_user=None):
     """ check token by mailman cookie validation algorithm """
-
     try:
         issued, keymac = marshal.loads(binascii.unhexlify(token))
         key, received_mac = keymac.split(':', 1)
@@ -62,6 +67,17 @@ def csrf_check(mlist, token):
             key, user = key.split('+', 1)
         else:
             user = None
+        if user:
+            # This is for CVE-2021-42097.  The token is a user token because
+            # of the fix for CVE-2021-42096 but it must match the user for
+            # whom the options page is requested.
+            raw_user = UnobscureEmail(urllib.unquote(user))
+            if options_user and options_user != raw_user:
+                syslog('mischief',
+                       'Form for user %s submitted with CSRF token '
+                       'issued for %s.',
+                       options_user, raw_user)
+                return False
         context = keydict.get(key)
         key, secret = mlist.AuthContextInfo(context, user)
         assert key
diff --git a/Mailman/Cgi/options.py b/Mailman/Cgi/options.py
index 1037f8f9..60b7d9b6 100644
--- a/Mailman/Cgi/options.py
+++ b/Mailman/Cgi/options.py
@@ -54,9 +54,6 @@ except NameError:
     True = 1
     False = 0
 
-AUTH_CONTEXTS = (mm_cfg.AuthListAdmin, mm_cfg.AuthSiteAdmin,
-                 mm_cfg.AuthListModerator, mm_cfg.AuthUser)
-
 
 def main():
     global _
@@ -124,15 +121,6 @@ def main():
         print doc.Format()
         return
 
-    if set(params) - set(safe_params):
-        csrf_checked = csrf_check(mlist, cgidata.getfirst('csrf_token'))
-    else:
-        csrf_checked = True
-    # if password is present, void cookie to force password authentication.
-    if cgidata.getfirst('password'):
-        os.environ['HTTP_COOKIE'] = ''
-        csrf_checked = True
-
     # Set the language for the page.  If we're coming from the listinfo cgi,
     # we might have a 'language' key in the cgi data.  That was an explicit
     # preference to view the page in, so we should honor that here.  If that's
@@ -169,6 +157,16 @@ def main():
             user = user[-1].strip()
 
     # Avoid cross-site scripting attacks
+    if set(params) - set(safe_params):
+        csrf_checked = csrf_check(mlist, cgidata.getfirst('csrf_token'),
+                                  Utils.UnobscureEmail(urllib.unquote(user)))
+    else:
+        csrf_checked = True
+    # if password is present, void cookie to force password authentication.
+    if cgidata.getfirst('password'):
+        os.environ['HTTP_COOKIE'] = ''
+        csrf_checked = True
+
     safeuser = Utils.websafe(user)
     try:
         Utils.ValidateEmail(user)
@@ -871,8 +869,9 @@ def options_page(mlist, doc, user, cpuser, userlang, message=''):
         mlist.FormatButton('othersubs',
                            _('List my other subscriptions')))
     replacements['<mm-form-start>'] = (
+        # Always make the CSRF token for the user. CVE-2021-42096
         mlist.FormatFormStart('options', user, mlist=mlist, 
-            contexts=AUTH_CONTEXTS, user=user))
+            contexts=[mm_cfg.AuthUser], user=user))
     replacements['<mm-user>'] = user
     replacements['<mm-presentable-user>'] = presentable_user
     replacements['<mm-email-my-pw>'] = mlist.FormatButton(
diff --git a/Mailman/SecurityManager.py b/Mailman/SecurityManager.py
index 9b7f03f3..e9e5ce53 100644
--- a/Mailman/SecurityManager.py
+++ b/Mailman/SecurityManager.py
@@ -104,6 +104,7 @@ class SecurityManager:
             if user is None:
                 # A bad system error
                 raise TypeError, 'No user supplied for AuthUser context'
+            user = Utils.UnobscureEmail(urllib.unquote(user))
             secret = self.getMemberPassword(user)
             userdata = urllib.quote(Utils.ObscureEmail(user), safe='')
             key += 'user+%s' % userdata
-- 
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