CVE-2025-21173

Local-system file write via insecure temporary file

Published Jan 14, 2025 · Updated Jun 9, 2026

Insecure temporary-file creation in Microsoft .NET 8.0 and 9.0 SDKs allows local users to write files as the local system on Linux. Microsoft's public advisory does not identify the SDK routine or disclose how the crafted file exploits the temporary-file permission error. Exploitation requires local low-privileged access and user interaction; the reported consequence is a file write in the local-system security context.

CVSS severity7.3
High
EPSS probability1.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insecure temporary-file creation in Microsoft .NET 8.0 and 9.0 SDKs allows local users to write files as the local system on Linux. Microsoft's public advisory does not identify the SDK routine or disclose how the crafted file exploits the temporary-file permission error. Exploitation requires local low-privileged access and user interaction; the reported consequence is a file write in the local-system security context.

The record

CVE
CVE-2025-21173
Published
Jan 14, 2025
Updated
Jun 9, 2026
Vendor
Microsoft
Product
.NET 9.0
Classifications
CWE-379, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 14, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.0.0 <9.0.1

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · .NET 9.0version=9.0.0 <9.0.1
Microsoft · Microsoft Visual Studio 2022 version 17.12version=17.12.0 <17.12.4
Microsoft · Microsoft Visual Studio 2022version=17.10.0 <17.10.10; version=17.6.0 <17.6.22; version=17.8.0 <17.8.17
Microsoft · .NET 8.0version=8.0.0 <8.0.12

Published CVSS scores

7.3Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-379Creation of Temporary File in Directory with Insecure Permissions
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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