CVE-2026-34459: Sandboxie-Plus Privilege Escalation Flaw

CVE-2026-34459 Overview

CVE-2026-34459 is a sandbox escape vulnerability in Sandboxie-Plus, an open source sandbox-based isolation tool for Windows. The flaw resides in the SbieSvc proxy service's GetRawInputDeviceInfoSlave handler and affects versions 1.17.2 and earlier. The handler contains two distinct defects: an information disclosure that leaks up to 32KB of uninitialized stack memory, and a stack buffer overflow [CWE-121] caused by an unchecked memcpy length. A sandboxed process can chain these flaws to defeat ASLR and /GS protections, then execute a Return-Oriented Programming (ROP) chain for SYSTEM privilege escalation. The exploit succeeds even from within a Security Hardened Sandbox.

Critical Impact

A sandboxed, low-privileged process can escape isolation and gain SYSTEM privileges on the host by chaining a stack memory leak with a stack buffer overflow in the SbieSvc service.

Affected Products

• Sandboxie-Plus versions 1.17.2 and earlier
• SbieSvc proxy service component
• Security Hardened Sandbox configurations on Windows hosts

Discovery Timeline

• 2026-05-05 - CVE-2026-34459 published to the National Vulnerability Database
• 2026-05-06 - Last updated in NVD database

Technical Details for CVE-2026-34459

Vulnerability Analysis

The vulnerability exists in the GetRawInputDeviceInfoSlave IPC handler implemented by SbieSvc, the privileged service that brokers operations on behalf of sandboxed processes. The handler accepts a request structure from sandboxed clients that includes a cbSize field controlling how much data the service writes back and reads. Two independent defects in this handler combine into a full sandbox escape and local privilege escalation chain.

The first defect is an uninitialized memory disclosure. When a sandboxed process submits an IPC request with cbSize set to 0, the handler returns up to 32KB of uninitialized stack memory belonging to the service process. This memory contains return addresses and /GS stack cookies, which the attacker uses to defeat Address Space Layout Randomization (ASLR) and stack canary protections.

The second defect is a classic stack buffer overflow. The handler invokes memcpy using an attacker-controlled length without verifying it fits inside the 32KB stack buffer. Combined with the leaked cookie and module bases, this enables reliable corruption of saved control data on the stack.

Root Cause

The root cause is missing input validation on IPC parameters from a lower-trust client. The handler trusts cbSize for both the response size and the subsequent copy length, and it does not zero-initialize the response buffer before transmitting it back to the sandboxed caller.

Attack Vector

A sandboxed process issues a crafted IPC request to SbieSvc with cbSize = 0 to harvest stack memory containing return addresses and the /GS cookie. The attacker then sends a second request with an oversized cbSize to overflow the 32KB stack buffer, overwriting the return address with a ROP chain that executes in the SYSTEM-privileged service. Hardware-enforced shadow stacks via Intel Control-flow Enforcement Technology (CET) block ROP execution but do not prevent the information leak.

No public proof-of-concept code is available. See the GitHub Security Advisory for the technical write-up.

Detection Methods for CVE-2026-34459

Indicators of Compromise

• Unexpected child processes spawned by SbieSvc.exe running as NT AUTHORITY\SYSTEM
• Crashes or access violations in SbieSvc.exe correlated with sandboxed process activity
• Sandboxed processes issuing high volumes of GetRawInputDeviceInfoSlave IPC requests

Detection Strategies

• Monitor parent-child process relationships where SbieSvc.exe spawns interactive shells, cmd.exe, powershell.exe, or LOLBins
• Hunt for token elevation events where a process originally launched inside a Sandboxie box later runs with SYSTEM integrity
• Inspect Windows Error Reporting and crash dumps for stack corruption faults inside SbieSvc.exe

Monitoring Recommendations

• Enable verbose Sandboxie logging and forward IPC trace events to a central SIEM for correlation
• Alert on installations of Sandboxie-Plus at or below version 1.17.2 across the fleet
• Track CET-incompatible hosts running Sandboxie-Plus, since they lack the shadow-stack mitigation against the ROP chain

How to Mitigate CVE-2026-34459

Immediate Actions Required

• Upgrade Sandboxie-Plus to version 1.17.3 or later on all Windows endpoints
• Inventory hosts running vulnerable versions (1.17.2 and earlier) and prioritize systems used to detonate untrusted code or browse high-risk content
• Restrict who can execute code inside Sandboxie boxes on multi-user systems until patching is complete

Patch Information

The maintainers fixed both the uninitialized stack disclosure and the unbounded memcpy in Sandboxie-Plus version 1.17.3. Refer to the Sandboxie-Plus GHSA-7cpc-5hv7-rfmh advisory for fix details and release notes.

Workarounds

• Enable Intel CET hardware-enforced shadow stacks on supported CPUs to block the ROP chain, while accepting that the information leak remains exploitable
• Stop the SbieSvc service on systems where Sandboxie-Plus is not actively required until the patch is deployed
• Avoid running untrusted code inside Sandboxie boxes on hosts that cannot be patched immediately

# Verify installed Sandboxie-Plus version on Windows (PowerShell)
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*" |
  Where-Object { $_.DisplayName -like "*Sandboxie*" } |
  Select-Object DisplayName, DisplayVersion, Publisher

# Stop the SbieSvc service as a temporary mitigation
sc.exe stop SbieSvc
sc.exe config SbieSvc start= disabled