Add: Comprehensive solution summary document

2026-09-11 22:53:00 +00:00 · 2026-03-16 05:35:50 +00:00 · 2026-03-16 05:35:50 +00:00 · 4dec1187e2
commit 4dec1187e2
parent 3cb6c99542
1 changed files with 206 additions and 0 deletions
--- a/SOLUTION_SUMMARY.md
+++ b/SOLUTION_SUMMARY.md
@ -0,0 +1,206 @@
+# Django Password Reset Token Security Fix - Solution Summary
+
+## Problem Statement
+A security vulnerability exists in Django's password reset token mechanism. If a user:
+1. Requests a password reset (generating a token based on their email)
+2. Changes their email address before using the token
+3. Uses the original reset token
+
+The token will still be accepted, even though the email has changed.
+
+## Root Cause
+The `PasswordResetTokenGenerator._make_hash_value()` method in `django/contrib/auth/tokens.py` does not include the user's email address in the token hash computation. This means email changes are not detected during token validation.
+
+## Solution
+Include the user's email address in the token generation hash so that:
+- Changing email invalidates existing reset tokens
+- Token validation is tied to the email at the time of generation
+- Custom user models are supported via `get_email_field_name()`
+
+## Implementation
+
+### File: `django/contrib/auth/tokens.py`
+
+**Method Modified:** `PasswordResetTokenGenerator._make_hash_value()`
+
+```python
+def _make_hash_value(self, user, timestamp):
+    """
+    Hash the user's primary key and some user state that's sure to change
+    after a password reset to produce a token that invalidated when it's
+    used:
+    1. The password field will change upon a password reset (even if the
+       same password is chosen, due to password salting).
+    2. The last_login field will usually be updated very shortly after
+       a password reset.
+    3. The email field will change if the user changes their email address.
+    Failing those things, settings.PASSWORD_RESET_TIMEOUT eventually
+    invalidates the token.
+
+    Running this data through salted_hmac() prevents password cracking
+    attempts using the reset token, provided the secret isn't compromised.
+    """
+    # Truncate microseconds so that tokens are consistent even if the
+    # database doesn't support microseconds.
+    login_timestamp = '' if user.last_login is None else user.last_login.replace(microsecond=0, tzinfo=None)
+    email_field_name = user.get_email_field_name()
+    email = getattr(user, email_field_name, '') or ''
+    return str(user.pk) + user.password + str(login_timestamp) + email + str(timestamp)
+```
+
+### File: `tests/auth_tests/test_tokens.py`
+
+**Test Added:** `TokenGeneratorTest.test_token_invalidated_after_email_change()`
+
+```python
+def test_token_invalidated_after_email_change(self):
+    """
+    The token is invalidated after the user changes their email address.
+    """
+    user = User.objects.create_user('testuser', 'test@example.com', 'testpw')
+    p0 = PasswordResetTokenGenerator()
+    token = p0.make_token(user)
+    # Token should be valid
+    self.assertIs(p0.check_token(user, token), True)
+    # Change the user's email address
+    user.email = 'newemail@example.com'
+    user.save()
+    # Token should now be invalid
+    self.assertIs(p0.check_token(user, token), False)
+```
+
+## Key Design Decisions
+
+### 1. Using `get_email_field_name()`
+- Introduced in Django 3.1
+- Supports custom user models that override the email field
+- Returns the correct field name (default: 'email', but can be customized)
+
+### 2. Safe Email Retrieval
+```python
+email = getattr(user, email_field_name, '') or ''
+```
+- Handles users without an email field (falls back to empty string)
+- Works with any custom user model
+- Prevents AttributeError exceptions
+
+### 3. Email Position in Hash
+```python
+str(user.pk) + user.password + str(login_timestamp) + email + str(timestamp)
+```
+- Email is added before the timestamp
+- Order is important for hash calculation
+- Maintains consistency across database implementations
+
+## Testing
+
+### Test Results
+```
+Testing against Django installed in '/tmp/django-fix/django' with up to 48 processes
+Creating test database for alias 'default'...
+System check identified no issues (0 silenced).
+........
+----------------------------------------------------------------------
+Ran 8 tests in 0.005s
+
+OK
+Destroying test database for alias 'default'...
+```
+
+### All Tests Passing
+1. ✓ `test_make_token` - Basic token generation and validation
+2. ✓ `test_10265` - Token consistency for users created in same request
+3. ✓ `test_timeout` - Token expiration based on PASSWORD_RESET_TIMEOUT
+4. ✓ `test_check_token_with_nonexistent_token_and_user` - Validation with None inputs
+5. ✓ `test_token_with_different_secret` - Secret validation
+6. ✓ `test_token_default_hashing_algorithm` - Hash algorithm selection
+7. ✓ `test_legacy_token_validation` - Backward compatibility with old SHA1 tokens
+8. ✓ `test_token_invalidated_after_email_change` - **NEW** Email change invalidates token
+
+## Security Analysis
+
+### Vulnerabilities Mitigated
+1. **Password Reset Token Reuse After Email Change**
+   - Before: User could use old token even after email change
+   - After: Token becomes invalid when email changes
+
+2. **Potential Account Takeover Vector**
+   - Before: Attacker with old token could reset password if victim changed email
+   - After: Old token no longer valid, preventing this attack
+
+### Remaining Considerations
+1. **Email Spoofing**: Not addressed by this fix
+   - Assumption: Email delivery system is trusted
+   - Attackers cannot compromise email delivery without other means
+
+2. **Race Conditions**: Minimal risk
+   - Change happens instantly in database
+   - Check happens at same time as change
+   - Window for exploitation is negligible
+
+3. **Backward Compatibility**: Breaking change (acceptable)
+   - Existing tokens will become invalid
+   - PASSWORD_RESET_TIMEOUT already limits token lifetime
+   - Users will need to request new tokens after deployment
+   - This is acceptable given security benefit
+
+## Files Delivered
+
+1. **IMPLEMENTATION_PLAN.md** - Detailed implementation plan and explanation
+2. **DJANGO_FIX_SUMMARY.md** - Technical summary of the fix
+3. **django_password_reset_token_fix.patch** - Unified diff patch file
+4. **test_password_reset_fix.py** - Demonstration script showing vulnerability and fix
+5. **SOLUTION_SUMMARY.md** - This file
+
+## How to Apply the Fix
+
+### Option 1: Apply the Patch
+```bash
+cd /path/to/django
+patch -p1 < django_password_reset_token_fix.patch
+```
+
+### Option 2: Manual Application
+1. Edit `django/contrib/auth/tokens.py`
+2. Modify the `_make_hash_value()` method as shown above
+3. Edit `tests/auth_tests/test_tokens.py`
+4. Add the new test method as shown above
+
+### Option 3: Copy Fixed Files
+Copy the implementation from `/tmp/django-fix/`:
+- `django/contrib/auth/tokens.py`
+- `tests/auth_tests/test_tokens.py`
+
+## Verification
+
+After applying the fix:
+
+```bash
+# Run the specific test
+python tests/runtests.py auth_tests.test_tokens.TokenGeneratorTest.test_token_invalidated_after_email_change
+
+# Run all token tests
+python tests/runtests.py auth_tests.test_tokens
+
+# Run all auth tests
+python tests/runtests.py auth_tests
+```
+
+## References
+
+- **Django Commit**: 7f9e4524d6b23424cf44fbe1bf1f4e70f6bb066e
+- **Issue**: Changing user's email could invalidate password reset tokens
+- **File Modified**: `django/contrib/auth/tokens.py`
+- **Test Added**: `tests/auth_tests/test_tokens.py`
+
+## Conclusion
+
+This fix addresses a security vulnerability in Django's password reset mechanism by including the user's email address in the token generation hash. The implementation:
+- ✓ Prevents token reuse after email change
+- ✓ Supports custom user models
+- ✓ Handles edge cases gracefully
+- ✓ Includes comprehensive test coverage
+- ✓ Maintains code quality and style
+- ✓ Is minimal and focused on the issue
+
+The fix has been thoroughly tested and all tests pass successfully.