Description
Improper preservation of permissions in the Avast sandbox minifilter driver (aswSnx.sys) on Windows allows a local, low-privileged attacker executing inside the sandbox to escape file isolation and escalate to SYSTEM.



When the sandbox virtualizes a file it copies the original security descriptor, but the driver opened the virtualization target object with GENERIC_WRITE and FILE_WRITE_ATTRIBUTES only, omitting WRITE_DAC. Every attempt to apply the original DACL therefore failed, and the failure was discarded silently, leaving virtualized copies of sensitive files with permissive permissions. Because the IRP_MJ_CREATE callback additionally did not strip WRITE_DAC for sensitive directories, a sandboxed process could rewrite the security descriptor of a virtualized object, read the virtualized copy of the SAM database, extract local NTLM password hashes and execute code as SYSTEM.



The absence of an IRP_MJ_SET_SECURITY callback in the driver's operation registration table is a related defense-in-depth gap, but it is not the control that prevents this attack.
Published: 2026-09-16
Score: 8.8 High
EPSS: < 1% Very Low
KEV: No
Impact: Local Privilege Escalation
Action: Immediate Patch
AI Analysis

Impact

The vulnerability is an improper preservation of permissions in the Avast sandbox minifilter driver. When the sandbox virtualizes a file, it copies the original security descriptor but opens the target object with only write‑attributes permissions, omitting WRITE_DAC. The driver silently discards failures when attempting to apply the original DACL, leaving virtualized copies with overly permissive permissions. An attacker limited to the sandbox can thus rewrite the security descriptor of a virtualized object, read the virtualized copy of the SAM database, extract local NTLM hashes, and execute code as SYSTEM. This flaw corresponds to improper authorization (CWE‑862) and missing DACL handling (CWE‑281, CWE‑653).

Affected Systems

The affected products are Gen Digital’s antivirus families: Avast Free Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security, AVG Free, AVG Internet Security, AVG Ultimate, Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, and Norton 360 Advanced. The flaw exists in the sandbox driver (aswSnx.sys for Avast, avgSnx.sys for AVG, nllSnx.sys for Norton) on all release lines older than 26.7. Micro‑updates released on September 4 2026 replace the driver with version 26.7.1021.0 for the 26.7 line and 26.8.1020.0 for the 26.8 line. Installations on earlier release lines do not receive these micro‑updates and remain vulnerable.

Risk and Exploitability

The CVSS score is 8.8 and the EPSS score is below 1 %, indicating a severe but unlikely mass exploitation. The vulnerability is local; an attacker must already have execution within the sandbox. The flaw is not listed in the CISA KEV catalog. Because the fix is a driver replacement, a device restart is required to load the new driver; until the restart the system remains exposed. When present, the updated driver prevents the privilege‑enhancement path by correctly preserving DACLs and handling WRITE_DAC permissions.

Generated by OpenCVE AI on September 18, 2026 at 03:15 UTC.

Remediation

Vendor Solution

Gen Digital has released a fix as an automatic micro-update to the sandbox driver. No product upgrade or reinstallation is required, and the product version number does not change. Because the fix replaces a kernel-mode driver, a device restart is required to load it. Until the device is restarted the previous driver stays active and the system remains vulnerable. The application notifies the user to restart. * 26.7 release line: fixed driver version 26.7.1021.0 * 26.8 release line: fixed driver version 26.8.1020.0 The update was published for Avast, AVG and Norton on 2026-09-04. Because the fix is delivered as a driver replacement rather than a product version increment, administrators who need to confirm remediation should verify that the running sandbox driver (aswSnx.sys on Avast, avgSnx.sys on AVG, nllSnx.sys on Norton) is at or above the fixed version after the restart, rather than checking the product version. Installations on release lines earlier than 26.7 do not receive these micro-updates and remain affected.

Vendor Workaround

Applying the driver micro-update described under Solution is the only complete remediation. Where that update cannot be applied, Gen Digital ships detection for exploitation attempts against this issue, so keeping product virus definitions current provides detection of the publicly released proof-of-concept. Detection of a known proof-of-concept is not equivalent to the code fix and does not prevent variants. Where the sandbox feature is not required, disabling it removes exposure to this attack path.

OpenCVE Recommended Actions

  • Install the micro‑update released on 2026‑09‑04, which replaces aswSnx.sys, avgSnx.sys, or nllSnx.sys depending on the product, and schedule a device restart to load the new driver.
  • If the micro‑update cannot be deployed, keep the latest virus‑definition database and rely on detection of the proof‑of‑concept; this does not prevent exploitation but provides early warning.
  • Disable the sandbox feature entirely when it is not required, which removes the attack path.

Generated by OpenCVE AI on September 18, 2026 at 03:15 UTC.

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History

Thu, 17 Sep 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Wed, 16 Sep 2026 14:30:00 +0000

Type Values Removed Values Added
Description Improper preservation of permissions in the Avast sandbox minifilter driver (aswSnx.sys) on Windows allows a local, low-privileged attacker executing inside the sandbox to escape file isolation and escalate to SYSTEM. When the sandbox virtualizes a file it copies the original security descriptor, but the driver opened the virtualization target object with GENERIC_WRITE and FILE_WRITE_ATTRIBUTES only, omitting WRITE_DAC. Every attempt to apply the original DACL therefore failed, and the failure was discarded silently, leaving virtualized copies of sensitive files with permissive permissions. Because the IRP_MJ_CREATE callback additionally did not strip WRITE_DAC for sensitive directories, a sandboxed process could rewrite the security descriptor of a virtualized object, read the virtualized copy of the SAM database, extract local NTLM password hashes and execute code as SYSTEM. The absence of an IRP_MJ_SET_SECURITY callback in the driver's operation registration table is a related defense-in-depth gap, but it is not the control that prevents this attack.
Title Avast sandbox privilege escalation via unpreserved DACLs on virtualized files in aswSnx.sys
Weaknesses CWE-281
CWE-653
CWE-862
References
Metrics cvssV3_1

{'score': 8.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H'}

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: GEN

Published:

Updated: 2026-09-17T18:42:28.924Z

Reserved: 2026-08-31T13:57:13.454Z

Link: CVE-2026-82964

cve-icon Vulnrichment

Updated: 2026-09-17T18:42:11.422Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-16T15:17:55.837

Modified: 2026-09-17T19:17:05.013

Link: CVE-2026-82964

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-18T03:30:02Z

Weaknesses
  • CWE-281

    Improper Preservation of Permissions

  • CWE-653

    Improper Isolation or Compartmentalization

  • CWE-862

    Missing Authorization