.NET 8.0: External Control of File Name or Path
CVE-2025-26646 is a high-severity external control of file name or path vulnerability in .NET 8.0 from Microsoft, with a CVSS 3.1 base score of 8.0 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, but only if a user takes part, for example by opening a link or file. The record lists version 8.0.16 as the first without the flaw, so updating .NET 8.0 to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.29% chance of exploitation within 30 days, higher than 71% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update .NET 8.0 to 8.0.16 or a later version.
- Update .NET 9.0 to 9.0.5 or a later version.
- Update Build Tools for Visual Studio 2022 to Fixed Version 17.13.7 or a later version.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | .NET 8.0 | 8.0.0 up to, but not including, 8.0.16 | 8.0.16 |
| Microsoft | .NET 9.0 | 9.0.0 up to, but not including, 9.0.5 | 9.0.5 |
| Microsoft | Build Tools for Visual Studio 2022 | 17.0 up to, but not including, Fixed Version 17.13.7 | Fixed Version 17.13.7 |
| Microsoft | Microsoft Visual Studio 2022 version 17.10 | 17.10.0 up to, but not including, 17.10.15 | 17.10.15 |
| Microsoft | Microsoft Visual Studio 2022 version 17.12 | 17.12.0 up to, but not including, 17.12.8 | 17.12.8 |
| Microsoft | Microsoft Visual Studio 2022 version 17.13 | 17.13.0 up to, but not including, 17.13.7 | 17.13.7 |
| Microsoft | Microsoft Visual Studio 2022 version 17.8 | 17.8.0 up to, but not including, 17.8.21 | 17.8.21 |
| Microsoft | Build Tools | before 17.13.7 | 17.13.7 |
| Microsoft | Visual Studio 2022 | 17.8.0 up to, but not including, 17.8.21; 17.10.0 up to, but not including, 17.10.15; 17.12.0 up to, but not including, 17.12.8; 17.13.0 up to, but not including, 17.13.7 | 17.8.21, 17.10.15, 17.12.8, 17.13.7 |
| Microsoft | .net | 9.0.0 up to, but not including, 9.0.5; 8.0.0 up to, but not including, 8.0.16 | 9.0.5, 8.0.16 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H. Scored by CNA (microsoft.com).
Official description
External control of file name or path in .NET, Visual Studio, and Build Tools for Visual Studio allows an authorized attacker to perform spoofing over a network.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: External Control of File Name or Path
The product allows user input to control or influence paths or file names that are used in filesystem operations.
How developers prevent this class of flaw
- When the set of filenames is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames, and reject all other inputs. For example, ID 1 could map to inbox.txt and ID 2 could map to profile.txt. Features such as the ESAPI AccessReferenceMap provide this capability.
- Run your code in a jail or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict all access to files within a particular directory. Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
More External Control of File Name or Path vulnerabilities (CWE-73)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in .NET 8.0
- 7.5 High severity
Recent External Control of File Name or Path vulnerabilities
- 7.5 High severity
- 8.1 High severity
- 8.8 High severity
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
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