Avast sandbox privilege escalation via unpreserved DACLs on virtualized files in aswSnx.sys

Summary

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.

Timeline

1. Sep 16, 2026, 2:01 PM UTCCVE published
2. Sep 17, 2026, 6:41 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: total

3. Sep 17, 2026, 6:42 PM UTCRecord last updated

Affected versions

• Gen Digital Avast Free Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security

  fixed in 26.8

• Gen Digital AVG Antivirus Free, AVG Internet Security, AVG Ultimate

  fixed in 26.8

• Gen Digital Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced

  fixed in 26.8

References 6