Runtime Changes for Migration from .NET Framework 4.6.1 to 4.6.2

Introduction

Runtime changes affect all apps that are running under a .NET Framework it was not compiled against and that use a particular feature.

In the topics that describe runtime changes, we have classified individual items by their expected impact, as follows:

Major This is a significant change that affects a large number of apps or that requires substantial modification of code.

Minor This is a change that affects a small number of apps or that requires minor modification of code.

Edge case This is a change that affects apps under very specific scenarios that are not common.

Transparent This is a change that has no noticeable effect on the app's developer or user. The app should not require modification because of this change.

If you are migrating from the .NET Framework 4.6.1 to 4.6.2, review the following topics for application compatibility issues that may affect your app:

Data

Attempting a TCP/IP connection to a SQL Server database that resolves to localhost fails

Details In the .NET Framework 4.6 and 4.6.1, attempting a TCP/IP connection to a SQL Server database that resolves to localhost fails with the error, "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)"
Suggestion This issue has been addressed and the previous behavior restored in the .NET Framework 4.6.2. To connect to a SQL Server database that resolves to localhost, upgrade to the .NET Framework 4.6.2.
Scope Minor
Version 4.6
Type Runtime

Connection pool blocking period for Azure SQL databases is removed

Details Starting with the .NET Framework 4.6.2, for connection open requests to known Azure SQL databases (*.database.windows.net, *.database.chinacloudapi.cn, *.database.usgovcloudapi.net, *.database.cloudapi.de), the connection pool blocking period is removed, and connection open errors are not cached. Attempts to retry connection open requests will occur almost immediately after transient connection errors. This change allows the connection open attempt to be retried immediately for Azure SQL databases, thereby improving the performance of cloud- enabled apps. For all other connection attempts, the connection pool blocking period continues to be enforced.

In the .NET Framework 4.6.1 and earlier versions, when an app encounters a transient connection failure when connecting to a database, the connection attempt cannot be retried quickly, because the connection pool caches the error and re-throws it for 5 seconds to 1 minute. For more information, see SQL Server Connection Pooling (ADO.NET). This behavior is problematic for connections to Azure SQL databases, which often fail with transient errors that are typically recovered from within a few seconds. The connection pool blocking feature means that the app cannot connect to the database for an extensive period, even though the database is available and the app needs to render within a few seconds.

Suggestion If this behavior is undesirable, the connection pool blocking period can be configured by setting the PoolBlockingPeriod property introduced in the .NET Framework 4.6.2. The value of the property is a member of the PoolBlockingPeriod enumeration that can take either of three values:The previous behavior can be restored by setting the PoolBlockingPeriod property to AlwaysBlock.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

Globalization

Unicode standard version 8.0 categories now supported

Details In .NET Framework 4.6.2, Unicode data has been upgraded from Unicode Standard version 6.3 to version 8.0. When requesting Unicode character categories in .NET Framework 4.6.2, some results might not match the results in previous .NET Framework versions. This change mostly affects Cherokee syllables and New Tai Lue vowels signs and tone marks.
Suggestion Review code and remove/change logic that depends on hard-coded Unicode character categories.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

Security

RSACng and DSACng are once again usable in Partial Trust scenarios

Details CngLightup (used in several higher-level crypto apis, such as System.Security.Cryptography.Xml.EncryptedXml) and System.Security.Cryptography.RSACng in some cases rely on full trust. These include P/Invokes without asserting SecurityPermissionFlag.UnmanagedCode permissions, and code paths where System.Security.Cryptography.CngKey has permission demands for SecurityPermissionFlag.UnmanagedCode. Starting with the .NET Framework 4.6.2, CngLightup was used to switch to System.Security.Cryptography.RSACng wherever possible. As a result, partial trust apps that successfully used System.Security.Cryptography.Xml.EncryptedXml began to fail and throw SecurityException exceptions.This change adds the required asserts so that all functions using CngLightup have the required permissions.
Suggestion If this change in the .NET Framework 4.6.2 has negatively impacted your partial trust apps, upgrade to the .NET Framework 4.7.1.
Scope Edge
Version 4.6.2
Type Runtime
Affected APIs

RSACng.VerifyHash now returns False for any verification failure

Details Starting with the .NET Framework 4.6.2, this method returns False if the signature itself is badly formatted. It now returns false for any verification failure.In the .NET Framework 4.6 and 4.6.1, the method throws a CryptographicException if the signature itself is badly formatted.
Suggestion Any code whose execution depends on handling the CryptographicException should instead execute if validation fails and the method returns False.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

SignedXml and EncryptedXml Breaking Changes

Details In .NET Framework 4.6.2, Security fixes in SignedXml and EncryptedXml lead to different run-time behaviors. For example,
  • If a document has multiple elements with the same id attribute and a signature targets one of those elements as the root of the signature, the document will now be considered invalid.
  • Documents using non-canonical XPath transform algorithms in references are now considered invalid.
  • Documents using non-canonical XSLT transform algorithms in references are now consider invalid.
  • Any program making use of external resource detached signatures will be unable to do so.
Suggestion Developers might want to review the usage of XmlDsigXsltTransform and XmlDsigXsltTransform, as well as types derived from Transform since a document receiver may not be able to process it.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

Windows Communication Foundation (WCF)

Remove Ssl3 from the WCF TransportDefaults

Details When using NetTcp with transport security and a credential type of certificate, the SSL 3 protocol is no longer a default protocol used for negotiating a secure connection. In most cases there should be no impact to existing apps as TLS 1.0 has always been included in the protocol list for NetTcp. All existing clients should be able to negotiate a connection using at least TLS1.0.
Suggestion If Ssl3 is required, use one of the following configuration mechanisms to add Ssl3 to the list of negotiated protocols.
Scope Edge
Version 4.6.2
Type Runtime
Affected APIs

Windows Presentation Foundation (WPF)

Changing the IsEnabled property of the parent of a TextBlock control affects any child controls

Details Starting with the .NET Framework 4.6.2, changing the IsEnabled property of the parent of a TextBlock control affects any child controls (such as hyperlinks and buttons) of the TextBlock control.In the .NET Framework 4.6.1 and earlier versions, controls inside a TextBlock did not always reflect the state of the IsEnabled property of the TextBlock parent.
Suggestion None. This change conforms to the expected behavior for controls inside a TextBlock control.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

CoerceIsSelectionBoxHighlighted

Details Certain sequences of actions involving a ComboBox and its data source can result in a NullReferenceException.
Suggestion If possible, upgrade to .NET Framework 4.6.2.
Scope Minor
Version 4.6
Type Runtime
Affected APIs

DataGridCellsPanel.BringIndexIntoView throws ArgumentOutOfRangeException

Details ScrollIntoView(Object) will work asynchronously when column virtualization is enabled but the column widths have not yet been determined. If columns are removed before the asynchronous work happens, an ArgumentOutOfRangeException can occur.
Suggestion Any one of the following:
  1. Upgrade to .NET Framework 4.7.
  2. Install the latest servicing patch for .NET Framework 4.6.2.
  3. Avoid removing columns until the asynchronous response to ScrollIntoView(Object) has completed.
Scope Edge
Version 4.6.2
Type Runtime
Affected APIs

Horizontal scrolling and virtualization

Details This change applies to an ItemsControl that does its own virtualization in the direction orthogonal to the main scrolling direction (the chief example is DataGrid with EnableColumnVirtualization="True"). The outcome of certain horizontal scrolling operations has been changed to produce results that are more intuitive and more analogous to the results of comparable vertical operations.

The operations include "Scroll Here" and "Right Edge", to use the names from the menu obtained by right-clicking a horizontal scrollbar. Both of these compute a candidate offset and call SetHorizontalOffset(Double).

After scrolling to the new offset, the notion of "here" or "right edge" may have changed because newly de-virtualized content has changed the value of ExtentWidth.

Prior to .NET Framework 4.6.2, the scroll operation simply uses the candidate offset, even though it may not be "here" or at the "right edge" any more. This results in effects like "bouncing" the scroll thumb, best illustrated by example. Suppose a DataGrid has ExtentWidth=1000 and Width=200. A scroll to "Right Edge" uses candidate offset 1000 - 200 = 800. While scrolling to that offset, new columns are de- virtualized; let's suppose they are very wide, so that the ExtentWidth changes to 2000. The scroll ends with HorizontalOffset=800, and the thumb "bounces" back to near the middle of the scrollbar - precisely at 800/2000 = 40%.

The change is to recompute a new candidate offset when this situation occurs, and try again. (This is how vertical scrolling works already.)

The change produces a more predictable and intuitive experience for the end user, but it could also affect any app that depends on the exact value of HorizontalOffset after a horizontal scroll, whether invoked by the end user or by an explicit call to SetHorizontalOffset(Double).

Suggestion An app that uses a predicted value for HorizontalOffset should be changed to fetch the actual value (and the value of ExtentWidth) after any horizontal scroll that could change ExtentWidth due to de-virtualization.
Scope Minor
Version 4.6.2
Type Runtime
Affected APIs

Items.Clear does not remove duplicates from SelectedItems

Details Suppose a Selector (with multiple selection enabled) has duplicates in its SelectedItems collection - the same item appears more than once. Removing those items from the data source (e.g. by calling Items.Clear) fails to remove them from SelectedItems; only the first instance is removed. Furthermore, subsequent use of SelectedItems (e.g. SelectedItems.Clear()) can encounter problems such as ArgumentException, because SelectedItems contains items that are no longer in the data source.
Suggestion Upgrade if possible to .NET Framework 4.6.2.
Scope Minor
Version 4.5
Type Runtime
Affected APIs

Item-scrolling a flat list with items of different pixel-height

Details When an ItemsControl displays a collection using virtualization (IsVirtualizing=true) and item- scrolling (ScrollUnit=Item), and when the control scrolls to display an item whose height in pixels differs from its neighbors, the VirtualizingStackPanel iterates over all items in the collection. The UI is unresponsive during this iteration; if the collection is large, this can be perceived as a hang.The iteration occurs in other circumstances, even in previous .NET Framework releases. For example, it occurs when pixel-scrolling (ScrollUnit=Pixel) upon encountering an item with different pixel height, and when item-scrolling hierarchical data (such as a TreeView or an ItemsControl with grouping enabled) upon encountering an item with a different number of descendant items than its neighbors.For the case of item-scrolling and different pixel height, the iteration was introduced in .NET Framework 4.6.1 to fix bugs in the layout of hierarchical data. It is not needed if the data is flat (no hierarchy), and .NET Framework 4.6.2 does not do it in that case.
Suggestion If the iteration occurs in .NET Framework 4.6.1 but not in earlier releases - that is, if the ItemsControl is item- scrolling a flat list with items of different pixel height - there are two remedies:
  1. Install .NET Framework 4.6.2.
  2. Install hotfix HR 1605 for .NET Framework 4.6.1.
Scope Minor
Version 4.6.1
Type Runtime
Affected APIs

RibbonGroup background is set to transparent in localized builds

Details RibbonGroup background on localized builds was always painted with Transparent brush, resulting in poor UI experience. This is fixed in .NET Framework 4.7 WPF fix by updating the localized resources for RibbonGroup, which in turn ensures that the correct brush is selected.
Suggestion Upgrade to .NET Framework 4.7
Scope Edge
Version 4.6.2
Type Runtime

WPF Spell Checking fails in unexpected ways

Details This includes a number of WPF Spell Checker issues:
  • WPF Spell Checker sometimes throws COMException
  • WPF Spell Checker fails with UnauthorizedAccessException when applications are launched using 'run as different user'
  • WPF Spell Checker incorrectly identifies spelling errors in compound words like 'Hausnummer' in German.
Suggestion Issue #1 - This has been fixed in .NET Framework 4.6.2 Issue #2 - WPF Spell Checker is no longer supported when applications are launched using 'run as different user'. Starting .NET Framework 4.6.2, applications launched in this manner will no longer crash unexpectedly - instead the Spell Checker will be silently disabled. Issue #3 - This has been fixed in .NET Framework 4.6.2.
Scope Edge
Version 4.6.1
Type Runtime