SMTP data disclosure via STARTTLS downgrade
Published Oct 14, 2025 · Updated Oct 14, 2025
Inadequate encryption in Microsoft .NET, .NET Framework, and Visual Studio allows man-in-the-middle attackers to read SMTP data. The SMTP client continues with plaintext delivery when an intermediary prevents TLS negotiation, rather than preserving transport encryption. Exploitation requires a network position between client and server and an application that sends SMTP traffic; confidentiality is the only reported impact.
Summary
What happened
Inadequate encryption in Microsoft .NET, .NET Framework, and Visual Studio allows man-in-the-middle attackers to read SMTP data. The SMTP client continues with plaintext delivery when an intermediary prevents TLS negotiation, rather than preserving transport encryption. Exploitation requires a network position between client and server and an application that sends SMTP traffic; confidentiality is the only reported impact.
The record
- CVE
- CVE-2025-55248
- Published
- Oct 14, 2025
- Updated
- Oct 14, 2025
- Vendor
- Microsoft
- Product
- Microsoft .NET Framework 3.5 and 4.8
- Classifications
- CWE-326, T1557
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Oct 14, 2025CVE publishedPublication date reported by the CVE source.
- Oct 14, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=4.8.0 <4.8.04798.02
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
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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