CVE-2025-55247: .NET Link Following Local Privilege Escalation Explained

Microsoft has published an advisory for CVE-2025-55247, a .NET elevation-of-privilege vulnerability rooted in improper link resolution before file access (commonly called “link following”), which can allow an authorized local user to escalate privileges on affected systems; industry trackers report a CVSS v3.1 base score of 7.3 (High) and Microsoft’s advisory is linked in public CVE feeds.

Background​

.NET is a foundational runtime and framework used widely across Windows desktops, servers, and cloud services. Vulnerabilities in the runtime can produce outsized risk because they affect large swaths of applications and services that depend on .NET’s file I/O, security, and hosting behaviors. Community analysis has repeatedly emphasized that an EoP in .NET is particularly dangerous for enterprise and developer environments because a local compromise can be rapidly amplified.
CVE-2025-55247 was publicly recorded on October 14, 2025, and is described as an improper link‑resolution vulnerability (CWE‑59) in .NET that allows an authorized local attacker to elevate privileges. Public vulnerability aggregators list the vulnerability and its CVSS vector indicating a local attack vector with low attack complexity but user interaction required in some variants.

---

What the vulnerability is (technical overview)​

The root class: CWE‑59 (Link following)​

This class of vulnerability occurs when code opens, reads, or writes files using a path supplied by an untrusted or insufficiently checked source, and fails to securely resolve symbolic links, junctions, or reparse points first. In practice this can allow an attacker to control where a privileged process actually performs file operations by creating or swapping links in the filesystem. When the privileged process follows that link without adequate checks, it performs file operations on an attacker-controlled target, enabling tampering or code execution depending on context.
CVE-2025-55247’s description specifically cites “improper link resolution before file access (‘link following’) in .NET,” which strongly implies a file I/O path-resolution bug in the runtime or in a common system library used by .NET that runs with elevated privileges.

Attack prerequisites and likely exploitation path​

• Prerequisite: Local access with an account that can run code or interact with the vulnerable .NET component. Public CVSS vectors indicate at least low privileges for the attacker in many configurations.
• Mechanics: The attacker creates a reparse point / symbolic link or races file operations so that a privileged .NET process opens/operates on an unexpected file (for example, a system config, service binary, or scheduled task file).
• Outcome: If the targeted operation allows write/replace of a privileged file or triggers execution of an attacker-controlled binary, the attacker can elevate to higher rights, including SYSTEM-level in worst-case scenarios.

Why this pattern is dangerous in .NET​

.NET hosts a large number of services and tooling (background services, Windows host processes, automated installers) that may perform file operations on behalf of elevated accounts. Where those operations accept paths influenced by lower‑privileged actors (e.g., temp folders, user-writable app data, or installation staging directories), a link‑following flaw can be a straightforward local privilege escalation primitive.

---

Affected products and status of patches​

Public aggregators list the MSRC advisory (the Microsoft Security Response Center entry) as the canonical record for CVE-2025-55247, and some feeds indicate patches have been released for recent .NET runtime branches (for example, .NET 8.x and 9.x in vendor-summarized notes), though the vendor bulletin's full product and build table may require direct inspection because MSRC pages are often JavaScript-rendered.
Important verification notes:

• Several trackers show a CVSS 3.1 base score of 7.3 and classify the vulnerability as local with high impact, but the public product list in some aggregators is incomplete or gated behind the vendor advisory view (which can require a browser to render fully). Administrators should consult the MSRC update guide directly (the MSRC entry referenced in aggregators) to confirm exact affected versions and KB/patch identifiers.
• Where vendor pages are client-side rendered, automated scrapers may not capture the full vulnerability table. Treat public aggregator product lists as indicative and confirm the authoritative MSRC advisory in a browser for exact KBs.

---

Exploitability and real‑world risk​

At publication:

• There are no widely reported proof‑of‑concepts (PoCs) or mass exploitation campaigns tied to CVE‑2025‑55247 in the open feeds. Aggregators currently rate exploitation probability as limited but possible if local conditions are present.
• The attack vector is local and the vulnerability requires the attacker to be able to influence file paths or create filesystem links that the privileged process later dereferences. This makes mass, unauthenticated remote exploitation unlikely, but the vulnerability is still highly relevant in environments where local access is possible (shared systems, multi-user servers, developer workstations, CI runners, or misconfigured service accounts).

Why defenders should care:

• Local privilege escalation is a common post‑compromise move; an attacker who gains a low‑privileged foothold (phished credential, malicious build job, or unpatched local service) can exploit EoP to escalate to SYSTEM and then persist or move laterally.
• Environments with automated build agents, shared developer boxes, or self‑service installers are high-risk because those components often interact with user-writable directories or staging areas.

---

Verification and cross-checking​

Multiple independent vulnerability trackers (CVE Details, CVEFeed, Feedly’s CVE feeds) list the same description and CVSS score for CVE‑2025‑55247, and they reference the MSRC advisory URL as the authoritative entry. This cross-corroboration gives a solid degree of confidence in the high-level technical description (link‑following / CWE‑59) and in the severity rating, but exact affected-version lists and KB numbers should be confirmed against the vendor advisory in a browser.
Flagging unverifiable claims:

• Several public feeds note “no affected products listed yet” in the aggregated view; if you see such a message, do not assume your environment is safe—check the MSRC advisory directly and confirm the runtime/package versions on your systems.

---

Immediate mitigation and remediation guidance​

Apply patching as the primary defense: Microsoft’s advisory (and aggregator notes) point to vendor updates for the .NET runtime branches. Administrators and developers should follow these steps immediately:

• Patch
• Apply the Microsoft security update(s) that fix CVE‑2025‑55247 for the .NET runtime versions in your estate. Confirm exact KB numbers and package versions on the MSRC advisory page.
• For containerized or packaged applications, rebuild images using patched .NET runtime images and redeploy.
• Inventory and verify
• Enumerate .NET runtimes on servers and workstations: use dotnet --list-runtimes and check installed framework versions on Windows via registry queries or package inventories.
• Map which services and background processes host .NET runtime code and whether those processes run with elevated privileges.
• Hardening and temporary mitigations (if patching will be delayed)
• Restrict local write access to directories used by privileged .NET processes (for example, installation staging directories, ProgramData locations, or service temp folders).
• Restrict who can create symbolic links or reparse points (Windows requires SeCreateSymbolicLinkPrivilege; minimize accounts with that privilege).
• Disable or firewall access to interactive and build/CI endpoints from untrusted users until patched.
• Where feasible, run .NET services with least privilege and avoid unnecessary SYSTEM-level contexts for components that can run as service accounts with constrained rights.
• Detection and monitoring
• Monitor for unexpected file replacement, reparse point creation, or changes in directories that privileged processes access.
• Instrument EDR to flag suspicious creation of symbolic links in locations used by privileged .NET processes, and hunt for process operations opening files following such links.
• Review Windows Event Logs and application logs for unexpected crashes, restarts, or file-access-denied patterns tied to .NET-hosted services.

---

Hunting and detection recipes (actionable)​

• File-system watches: alert on creation of symbolic links, junctions, or reparse points under:
• %ProgramFiles%, %ProgramData%, and service-specific staging folders
• Build agent working directories and CI runner temporary directories
• Process-to-file correlation: alert when privileged processes (services running as SYSTEM or high-privilege service accounts) open files that were recently created or re‑pointed by lower-privileged users.
• Behavioral patterns: watch for post‑exploit behaviors tied to EoP: unexpected creation of scheduled tasks, modification of service configuration, or placement of new binaries in protected locations.

These detection rules should be integrated into SIEM/EDR with context-aware thresholds to reduce false positives while catching high-fidelity indicators of a link‑following exploit attempt.

---

Developer and DevOps guidance​

• Audit code paths where applications accept file paths from users or other processes and then perform privileged operations. Apply canonical defenses:
• Canonicalize and resolve paths safely before use, and verify that the resolved target is within an expected directory tree.
• Use explicit privileges separation: avoid running installers or file‑manipulation code as SYSTEM when not required.
• Use secure API variants that can refuse to follow links or provide safe file open semantics where available.
• For CI/CD:
• Isolate build runners and restrict what files they can write or link to. Avoid running build jobs on machines that also host privileged services.
• Rebuild and redeploy containers and images based on patched base runtimes immediately after vendor updates are released.

---

Organizational risk assessment​

• Small teams and single‑user developer machines: risk is real but the attack requires local access; mitigate by keeping developer machines patched and restricting shared accounts.
• Enterprise servers and multi‑tenant builds: high risk. Shared build agents, CI runners, and developer workstations provide favorable conditions for an attacker to get the limited local access needed to exploit link‑following primitives.
• Cloud-hosted Windows images and PaaS hosts: verify if hosted service images include vulnerable runtime versions; patch images and redeploy. Azure and other cloud UI pages may also reference MSRC advisory details—confirm through vendor-managed update channels.

---

Why this vulnerability matters beyond its immediate technical mechanics​

Link‑following issues are simple to understand but often subtle to fix comprehensively in large codebases. They bridge a conceptual gap between filesystem semantics and application logic. In the context of .NET, the attack surface is amplified because:

• .NET is used by both end‑user apps and server components.
• Many administrative utilities and installers use .NET for convenience and scripting, sometimes running with elevated rights.
• The same runtime code paths can be shared across many products, producing wide blast radii when a core behavior needs patching.

Community commentary has stressed similar points during prior .NET EoP advisories: a single flaw in a common runtime or library yields systemic risk and forces coordinated patching across dev, ops, and security teams.

---

Practical checklist (first 48 hours)​

• Confirm MSRC advisory details for CVE‑2025‑55247 and note the exact KB / package IDs.
• Patch all .NET runtimes and rebuild container images that embed .NET base images.
• Block or isolate shared CI/build runners and developer machines until patched.
• Hunt for symbolic link creation in high‑value directories and alert on service file modifications.
• Apply least-privilege changes to services that host .NET code; remove unnecessary SYSTEM context where possible.
• Document and report any suspicious findings to incident response with relevant logs and timeline.

---

Conclusion​

CVE‑2025‑55247 is a high‑impact local elevation‑of‑privilege vulnerability in the .NET ecosystem caused by improper link resolution (CWE‑59). While the attack requires local access, the ubiquity of .NET and common use patterns for privileged installers and background services make this a serious issue for enterprises, developer workstations, and CI infrastructures. Public trackers report a CVSS 3.1 base score of 7.3, and vendor advisories should be consulted immediately for the exact affected versions and patches.
The core defensive posture is straightforward and time‑tested: patch quickly, reduce local attack surface, and harden file‑system and process privileges. Given the nature of link‑following flaws, defenders should assume the vulnerability can be weaponized in post‑compromise scenarios and act accordingly to protect build systems, shared developer hosts, and any service that accepts local file‑path input.

---

---

Source: MSRC Security Update Guide - Microsoft Security Response Center