CVE-2026-81963
Improper link resolution before file access ('link following') in Windows Update Stack allows an authorized attacker to elevate privileges locally.
High
Known exploited
- Severity
- 7.8 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.39%
- Chance of exploitation in the next 30 days. Higher than 33.55% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Sep 8, 2026
- Weakness
- CWE-59 Improper Link Resolution Before File Access ('Link Following')
- CWE-284 Improper Access Control
- Fix
- None yet
- No fixed version published
Exploited in the wild. Microsoft Windows Link Following Vulnerability (Microsoft Windows). Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Due for U.S. federal agencies by Sep 22, 2026.
Description
Improper link resolution before file access ('link following') in Windows Update Stack allows an authorized attacker to elevate privileges locally.
How to fix
No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.
Severity breakdown
CVSS 3.1 7.8
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-59: Improper Link Resolution Before File Access ('Link Following')
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
How to prevent it
- Architecture and Design: Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
CWE-284: Improper Access Control
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
How to prevent it
- Architecture and Design, Operation: Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
- Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
References
Advisories
Other links
Timeline
- Added to CISA's Known Exploited Vulnerabilities catalog
- Published
- Last updated by the source
- Remediation due for U.S. federal agencies
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-hjqx-j4rw-g7xv zip: Arbitrary file write outside the extraction directory, because ZipArchive::extract validates symlink targets lexically. | High | Same weakness, CWE-59 |
| GHSA-4vjg-vx72-qq4g systeminformation has path traversal in Linux networkStats() that allows symlink-based file disclosure outside /sys/class/net | Low | Same weakness, CWE-59 |
| GHSA-9j6q-wvj5-jgjg filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker | Low | Same weakness, CWE-59 |
| GHSA-j8f7-rjxc-mr56 filelock: ReadWriteLock follows a symlink at the lock path into SQLite | Medium | Same weakness, CWE-59 |
| GHSA-crv4-6mhj-j5jh filelock: SoftFileLock stale-break restore follows a swapped-in symbolic link and hard-links a file of the user running the lock into the lock directory | Medium | Same weakness, CWE-59 |
| GHSA-v4x8-3wr5-3wq8 filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files | High | Same weakness, CWE-59 |
| GHSA-gq48-pqfc-9p58 GitPython: Submodule.move() follows an attacker-committed intermediate symlink outside the worktree | Medium | Same weakness, CWE-59 |
| GHSA-2j93-m82w-73j2 Microsoft Security Advisory CVE-2026-96231 - .NET and Visual Studio Elevation of Privilege Vulnerability | High | Same weakness, CWE-59 |
MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.
Check your repos with MergeHarbor