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.
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.
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.