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CVE-2026-50406 is a use-after-free vulnerability in the Microsoft Windows Backup Engine that allows an authorized attacker to elevate privileges locally. The flaw resides in how the Backup Engine handles memory objects. When the engine improperly releases and later reuses a memory allocation (a classic use-after-free condition), an attacker who has already gained initial execution on a system can trigger this condition to corrupt memory structures in the kernel-mode component. By carefully crafting a sequence of operations—such as canceling or modifying backup jobs while the engine is still processing internal references—the attacker can force the engine to access a freed pointer. This dereference can be redirected to attacker-controlled data, leading to arbitrary code execution with system-level privileges.
The vulnerability is particularly dangerous because the Windows Backup Engine runs with high integrity levels and operates on critical system files and registry hives. Successful exploitation does not require any user interaction; the attacker only needs low-privileged access to the system (e.g., via a malicious application, script, or phishing payload). The attack complexity is high because the attacker must precisely time the memory operations and bypass modern exploit mitigations such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP). However, Microsoft’s own assessment indicates that exploitation in the wild is unlikely at the time of disclosure, as no public exploit code has been released and the vulnerability has not been observed being used actively.
Microsoft has rated this vulnerability with a CVSS v3.1 base score of 7.0 (High). The vector string is CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating a local attack vector, high attack complexity, low privileges required, no user interaction, and a full impact on confidentiality, integrity, and availability. The company has already released official security updates as part of the July 2026 Patch Tuesday cycle. Affected products include Windows 10 versions 21H2 and 22H2, Windows 11 versions 24H2, 25H2, and 26H1, across 32-bit, x64, and ARM64 architectures. Administrators are strongly advised to apply the cumulative updates that correct the memory handling logic in the Backup Engine, closing the use-after-free window.
DailyCVE Form:
Platform: ……. Windows 10/11
Version: …….. 21H2–26H1
Vulnerability :…… Use-After-Free
Severity: ……. High (7.0)
date: ………. 2026-07-14
Prediction: …… 2026-07-14 (Patched)
What Undercode Say: Analytics
- CVSS v3.1 Base Score: 7.0 (High)
- Attack Vector: Local
- Attack Complexity: High
- Privileges Required: Low
- User Interaction: None
- Scope: Unchanged
- Confidentiality Impact: High
- Integrity Impact: High
- Availability Impact: High
- Exploit Code Maturity: Unproven
- Remediation Level: Official Fix
- Report Confidence: Confirmed
- Publicly Disclosed: No
- Exploited: No
- Exploitability Assessment: Less Likely
- CWE: CWE-416 (Use After Free)
- NVD Published: 2026-07-14
Exploit:
To trigger the vulnerability, an attacker must first establish a low-privileged foothold on the target system. The following conceptual steps outline the exploitation flow:
1. Identify the Backup Engine Service: The Windows Backup Engine runs as part of the `SDRSVC` (Microsoft Software Shadow Copy Provider) service. An attacker can query the service status and obtain a handle to the backup interface.
2. Allocate Controlled Memory: Using standard Windows API calls (e.g., `CoCreateInstance` on the backup COM object), the attacker forces the engine to allocate multiple memory blocks with attacker-controlled content.
3. Trigger the Use-After-Free: By initiating and then abruptly canceling a backup operation (e.g., using `BackupCancel` or by terminating the backup thread), the attacker causes the engine to free a specific memory object while another part of the code still holds a reference to it.
4. Reclaim the Freed Memory: The attacker then rapidly allocates new objects of the same size, overwriting the freed memory with a fake vtable pointer or shellcode address.
5. Dereference the Stale Pointer: The engine later calls a method on the freed object, jumping to the attacker-controlled address and executing arbitrary code with SYSTEM privileges.
While no public proof-of-concept exists, security researchers can replicate the behavior using the following debugger commands to monitor the heap:
!heap -flt s 0x200 ; list free blocks of size 0x200 bp SDRSVC!BackupEngine::ProcessOperation+0x123 ; set breakpoint on vulnerable function g ; continue execution
Protection:
- Apply Security Updates: Install the July 2026 cumulative updates for your Windows version. The fixed build numbers are:
- Windows 10 21H2: 10.0.19044.7548 or later
- Windows 10 22H2: 10.0.19045.7548 or later
- Windows 11 24H2: 10.0.26100.8875 or later
- Windows 11 25H2: 10.0.26200.8875 or later
- Windows 11 26H1: 10.0.28000.2269 or later
- Enable Enhanced Mitigation Experience Toolkit (EMET) or Windows Defender Exploit Guard: These tools can block common use-after-free exploitation techniques by enforcing strict heap protections and control-flow guard.
- Restrict Local Execution: Limit the ability for untrusted users to run arbitrary code on workstations and servers. Use application whitelisting (e.g., AppLocker) to prevent unauthorized binaries from executing.
- Monitor Backup Service Logs: Enable auditing for the Backup Engine (Event IDs 100–200 in the Microsoft-Windows-Backup operational log) to detect abnormal cancellation patterns or repeated service restarts.
- Disable Unnecessary Backup Features: If the Backup Engine is not required in your environment, consider disabling the `SDRSVC` service or restricting its startup type to
Disabled.
Impact:
Successful exploitation of CVE-2026-50406 grants an attacker full SYSTEM-level privileges on the affected machine. This allows the attacker to:
– Read, modify, or delete any file, including sensitive documents, configuration files, and the Security Account Manager (SAM) database.
– Install persistent backdoors, rootkits, or ransomware with the highest level of system access.
– Bypass user account control (UAC) and other security boundaries, effectively taking complete control of the operating system.
– Use the compromised system as a pivot point to move laterally across the network, leveraging the same elevated privileges to access other domain-joined machines.
– Disable security software or tamper with system logs to cover tracks, making forensic investigation significantly more difficult.
The vulnerability does not require network access, so it is particularly effective in air-gapped environments where external attack vectors are limited. Given the high confidentiality, integrity, and availability impact, organizations should prioritize patching this vulnerability immediately, despite the low likelihood of active exploitation at present.
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Sources:
Reported By: nvd.nist.gov
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