Dynamic Data Exchange (DDE) is a Windows protocol that lets applications exchange information through messages and shared memory. It can transfer a value once or keep data linked so an application can receive updates. DDE has legitimate uses, but its command-execution feature has also been abused in malicious Office documents.
How does DDE work?
A DDE exchange is a conversation between a client and a server. The client initiates the conversation; the server responds. These are roles within a conversation, not permanent labels: an application can be a client in one exchange and a server in another.
The conversation identifies the data through three parts: the service (usually the server application), a topic that groups related data, and an item that identifies the particular value. For example, a spreadsheet could connect to a database service, use a topic for a dataset, and request a particular item.
DDE uses Windows messages to coordinate the exchange and shared memory to carry larger data. The protocol defines messages for initiating and ending conversations, requesting and sending data, notifying clients about updates, and executing commands. Message parameters can refer to atoms and shared-memory handles, so software that implements DDE must follow the protocol’s rules for ownership and cleanup. Microsoft’s overview of Dynamic Data Exchange describes these concepts and message types.
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What kinds of exchanges can DDE support?
DDE can handle a one-time request or an ongoing link between applications. With an update link, the client can receive notice that data changed and then request the new value (a warm link), or receive the changed value directly (a hot link). The link remains active until the client or server ends it, or the conversation terminates.
- Request: A client asks a server for a particular item.
- Data transfer: One application sends data to the other as part of a conversation.
- Update link: A client subscribes to changes, using either notification followed by a request or direct delivery of changed data.
- Command: A client can send a command for the server to execute.
What is DDEML?
The Dynamic Data Exchange Management Library (DDEML) is Microsoft’s higher-level API for managing DDE conversations, strings, and data. It handles much of the management involved in DDE, rather than requiring an application to work directly with the protocol’s messages and their associated resources.
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Microsoft recommends DDEML for new applications. It remains compatible with applications that use message-based DDE, so the two approaches can interoperate. The choice is therefore mainly about implementation: direct message handling gives an application responsibility for the protocol details, while DDEML provides a management layer. Microsoft’s DDEML documentation explains the library and its relationship to message-based DDE.
What is DDE used for?
Microsoft documents DDE uses that connect applications or keep related information synchronized, including:
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- Receiving real-time data, such as stock quotes or readings from scientific instruments.
- Keeping a chart embedded in a word-processing document synchronized with its source.
- Letting a spreadsheet query a database.
In these examples, DDE provides a way for separate programs to request, send, or update information. The client/server terminology and related DDE concepts are also described in Microsoft’s basic concepts for DDE.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is DDE dangerous in Office documents?
DDE itself is an interapplication communication protocol, not inherently malicious. However, because it supports command execution, attackers have used DDE commands in malicious Office documents. CISA describes cases in which such documents appeared in phishing campaigns or on web content and used DDE to deliver execution without relying on VBA macros. This is a documented abuse of DDE’s capabilities, not evidence that every DDE link or application using DDE is unsafe. CISA’s technique entry on Dynamic Data Exchange summarizes this abuse path.
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How does DDE differ from DDEML?
| Approach | How it works | Implementation responsibility |
|---|---|---|
| Message-based DDE | Applications handle DDE messages directly. | The application must manage protocol details, including message-related atoms and shared-memory ownership and cleanup. |
| DDEML | Microsoft’s management library provides a higher-level API for DDE conversations, strings, and data. | The library simplifies that management; Microsoft recommends this approach for new applications. It is compatible with message-based DDE. |
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