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How CVE-2026-49791 Works
CVE-2026-49791 is an elevation of privilege vulnerability in the Windows Routing and Remote Access Service (RRAS), stemming from improper link resolution before file access — a flaw classified under CWE-59 (Improper Link Resolution Before File Access, commonly known as “Link Following”).
At its core, the vulnerability exists because RRAS, a privileged Windows service, accesses files or directories using paths without properly validating whether those paths point to a symbolic link, junction point, mount point, or other type of redirection. An attacker with low-privileged, authenticated local access can exploit this by creating a specially crafted link that redirects the service to an unintended file or directory.
When RRAS subsequently performs operations on this redirected target — such as writing, modifying, replacing, or deleting files — it does so with SYSTEM-level privileges. By controlling the target of the link, the attacker can trick RRAS into modifying protected system resources that they would otherwise not have permission to touch. This effectively allows a standard user account to interfere with critical operating system components, leading to full system compromise.
The attack vector is local (AV:L) and requires low attack complexity (AC:L). The attacker must already have low privileges (PR:L) on the target machine, and no user interaction (UI:N) is required. Microsoft’s CVSS 3.1 vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H, giving it a base score of 7.1 (High). While confidentiality impact is rated none, both integrity and availability are rated high — meaning successful exploitation allows significant modification of system files or disruption of the host.
This vulnerability is particularly dangerous in post-compromise scenarios: an attacker who gains an initial foothold via phishing, stolen credentials, or another vulnerability can use CVE-2026-49791 to elevate from a restricted user-level context to SYSTEM-level privileges. Microsoft confirmed the vulnerability’s existence and rated it Important rather than Critical due to the local access requirement. No active exploitation in the wild was known at the time of disclosure.
DailyCVE Form
| Field | Value |
|-|-|
| Platform | Windows RRAS |
| Version | 10.0, 6.2, 6.3 |
| Vulnerability | Link Following (CWE-59) |
| Severity | 7.1 (High) |
| Date | 2026-07-14 |
| Prediction | 2026-07-14 (Released) |
What Undercode Say: Analytics
Check if the system is vulnerable by verifying the RRAS service state and OS build number systeminfo | findstr /B "OS Name OS Version" Enumerate symbolic links and junctions in system directories that RRAS might access dir /AL /S C:\Windows\System32\ 2>nul | findstr /i "JUNCTION SYMLINK" Check for the presence of the RRAS service (RemoteAccess) sc query RemoteAccess | findstr STATE Verify installed updates (look for July 2026 cumulative updates) wmic qfe list brief /format:table | findstr "2026-07"
Key Analytics Insight:
The vulnerability leverages CWE-59, meaning RRAS does not safely verify whether a path resolves to a symlink, junction, or mount point before performing privileged file operations. Microsoft’s fix involved adding proper link validation checks within the RRAS file-access routines.
How Exploit: Technical Walkthrough
A successful exploit follows this general pattern:
- Establish Low-Privilege Access – The attacker gains an initial foothold on the target system as a standard, authenticated user (e.g., via phishing or malware).
- Identify a Vulnerable RRAS Operation – The attacker locates a file or directory path that RRAS accesses with high privileges, but where the service does not validate link targets beforehand.
- Create a Malicious Link – Using standard Windows APIs (
CreateSymbolicLink,mklink, or junction points), the attacker places a symbolic link or junction at the path RRAS will access. The link points to a protected system resource (e.g.,C:\Windows\System32\config\SAM, a critical driver file, or a system binary). - Trigger RRAS – The attacker invokes the vulnerable RRAS functionality (e.g., through local RPC calls, management interfaces, or configuration changes) that causes the service to access the malicious link.
- Privileged File Operation – RRAS, running as SYSTEM, follows the link and performs a write, delete, or replace operation on the attacker-chosen target.
- Achieve SYSTEM Privileges – By overwriting a protected file (e.g., a service binary, a DLL, or the SAM hive), the attacker can implant malicious code or modify security policies, ultimately gaining full control over the system.
No user interaction is required after the initial foothold, and the low complexity means exploitation is reliable under normal conditions.
Protection: Mitigations and Remediation
| Mitigation | Description |
||-|
| Apply Security Update | Install the July 2026 Patch Tuesday cumulative update released on 2026-07-14. This update adds proper link resolution validation in RRAS. |
| Restrict Local Access | Limit the number of authenticated users on sensitive systems. Since the attack requires local low-privileged access, reducing the user base reduces attack surface. |
| Enable Windows Defender Credential Guard | Helps protect against credential theft and some post-exploitation techniques, though it does not directly prevent link-following. |
| Monitor for Suspicious Link Creation | Use Sysmon or Windows Event Logs to monitor for creation of symbolic links (Event ID 1 with `CreateSymbolicLink` or NtCreateSymbolicLinkObject) in system directories. |
| Principle of Least Privilege | Ensure that users do not have unnecessary local logon rights. Restrict who can interact with RRAS management interfaces. |
| Audit RRAS Activity | Monitor RRAS-related events and file access patterns for anomalies, especially writes to protected system paths. |
Impact: What Happens If Exploited
- System Compromise – An attacker can elevate from a standard user to SYSTEM privileges, gaining full administrative control over the affected machine.
- Integrity Violation – Protected system files, registry hives, or security configurations can be modified or replaced, allowing persistent backdoors, disabling of security controls, or tampering with audit logs.
- Availability Disruption – Critical system files can be corrupted or deleted, leading to denial of service, blue-screen conditions, or unbootable systems.
- Lateral Movement – Once SYSTEM is achieved, the attacker can extract credentials, move laterally across the network, and compromise additional hosts.
- No Remote Exploitation – The vulnerability is not remotely exploitable; it requires prior local access. However, in a kill-chain scenario, it serves as a powerful privilege-escalation step after an initial remote foothold.
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Sources:
Reported By: nvd.nist.gov
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