Authenticated message spoofing during SMTP routing
Published Jul 14, 2026 · Updated Jul 14, 2026
Improper output encoding in Microsoft .NET and Visual Studio allows remote authenticated users to spoof messages during SMTP routing. The flaw is in the System.Net.Mail SMTP client, but Microsoft has not disclosed which output field is encoded or escaped incorrectly. Exploitation requires network access and low privileges in an application that uses an affected runtime to route mail; it can alter message integrity without reported disclosure or service interruption.
Summary
What happened
Improper output encoding in Microsoft .NET and Visual Studio allows remote authenticated users to spoof messages during SMTP routing. The flaw is in the System.Net.Mail SMTP client, but Microsoft has not disclosed which output field is encoded or escaped incorrectly. Exploitation requires network access and low privileges in an application that uses an affected runtime to route mail; it can alter message integrity without reported disclosure or service interruption.
The record
- CVE
- CVE-2026-50659
- Published
- Jul 14, 2026
- Updated
- Jul 14, 2026
- Vendor
- Microsoft
- Product
- .NET 9.0
- Classifications
- CWE-116, T1656
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 14, 2026CVE publishedPublication date reported by the CVE source.
- Jul 14, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=9.0.0 <9.0.18
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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