CVE-2026-62776 Overview
CVE-2026-62776 is a local privilege escalation vulnerability in the Windows Dynamic Host Configuration Protocol (DHCP) Server service. The flaw stems from improper link resolution before file access, categorized as [CWE-59] link following. An authorized attacker with local access can abuse symbolic or hard links to redirect privileged file operations performed by the DHCP Server. Successful exploitation permits the attacker to elevate privileges on the affected host and gain broader control over the system.
Critical Impact
An authenticated local attacker can escalate privileges on a Windows DHCP Server host, resulting in high impact to confidentiality, integrity, and availability.
Affected Products
- Windows DHCP Server (specific supported Windows Server versions listed in the vendor advisory)
- Refer to the Microsoft CVE-2026-62776 Advisory for the authoritative product list
Discovery Timeline
- 2026-08-11 - CVE-2026-62776 published to the National Vulnerability Database (NVD)
- 2026-08-12 - Entry last modified in NVD
Technical Details for CVE-2026-62776
Vulnerability Analysis
The Windows DHCP Server service performs file operations under a privileged security context. The service resolves file paths without adequately validating whether path components are symbolic links, junctions, or hard links. A local user who can influence the target path or a directory in the resolution chain can redirect the service to a file the user could not otherwise modify. This class of flaw is tracked as [CWE-59], improper link resolution before file access. The Microsoft advisory classifies the resulting outcome as elevation of privilege with high impact across confidentiality, integrity, and availability.
Root Cause
The root cause is a missing or insufficient check to ensure that file paths accessed by the DHCP Server point to expected, non-linked filesystem objects. When the service opens, writes, or replaces files, an attacker-controlled reparse point can redirect the operation to an arbitrary location. Because the DHCP Server runs with elevated privileges, the redirected write inherits that privilege.
Attack Vector
Exploitation requires local access and low-privilege authentication on the target host. No user interaction is needed. The attacker plants a symbolic link, junction, or hard link in a filesystem location touched by the DHCP Server service, then triggers a service operation that follows the link. The service performs its file action on the attacker-chosen target, enabling arbitrary file write or overwrite as NT AUTHORITY\SYSTEM and subsequent privilege escalation.
No public proof-of-concept code is available. See the Microsoft CVE-2026-62776 Advisory for vendor technical detail.
Detection Methods for CVE-2026-62776
Indicators of Compromise
- Creation of symbolic links, junctions, or hard links by non-administrative users in directories accessed by the DHCP Server service.
- Unexpected file writes or replacements in system directories performed by the DHCP Server process (dhcpserver.exe or associated service host).
- New or modified files in privileged paths whose owner or timestamp aligns with DHCP Server service activity initiated by a low-privileged session.
Detection Strategies
- Monitor for NtCreateFile and reparse point operations originating from user-writable directories that are subsequently accessed by DHCP Server.
- Alert on privileged file writes by DHCP Server to paths outside its normal working set, such as System32 binaries or scheduled task definitions.
- Correlate low-privilege process activity that stages reparse points with immediate DHCP Server service actions on the same paths.
Monitoring Recommendations
- Enable Windows object access auditing on DHCP Server data and configuration directories, including %SystemRoot%\System32\dhcp\.
- Ingest Sysmon events for FileCreate, FileCreateStreamHash, and process activity from the DHCP Server service into a central log platform.
- Track service restarts, crashes, and configuration reload events on DHCP Server hosts, which may accompany exploitation attempts.
How to Mitigate CVE-2026-62776
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-62776 Advisory to all Windows Server hosts running the DHCP Server role.
- Restrict interactive and remote logon rights on DHCP Server hosts to administrators and required service accounts only.
- Audit local group membership and remove standard users from any DHCP Server that also serves general-purpose workloads.
Patch Information
Microsoft has issued a security update addressing CVE-2026-62776. Administrators should install the update through Windows Update, Windows Server Update Services (WSUS), or Microsoft Update Catalog. Consult the Microsoft CVE-2026-62776 Advisory for the specific KB article and build numbers that apply to each supported Windows Server release.
Workarounds
- Isolate the DHCP Server role on dedicated hosts that do not permit interactive logon by non-administrative users.
- Disable the SeCreateSymbolicLinkPrivilege right for non-administrative accounts on servers where it is not required.
- Constrain filesystem permissions on DHCP working directories so that only the DHCP service account and administrators can create files or links.
# Example: remove SeCreateSymbolicLinkPrivilege from non-admin users via secedit
# Export current policy, edit, and reapply
secedit /export /cfg C:\policy.cfg
# Edit C:\policy.cfg and ensure SeCreateSymbolicLinkPrivilege is restricted to *S-1-5-32-544 (Administrators)
secedit /configure /db C:\Windows\security\local.sdb /cfg C:\policy.cfg /areas USER_RIGHTS
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
