CVE-2026-82964
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.16%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- EPSS
- 0.16% probability · 5th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-281, CWE-653, CWE-862
- Source
- security@nortonlifelock.com
EPSS 0.2% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/MSNightmare/PrettyPrague
- https://support.avast.com/en-us/article/Update-Antivirus
- https://support.avg.com/SupportArticleView?l=en&urlname=Update-AVG-Antivirus
- https://support.norton.com/sp/en/us/home/current/solutions/v20240108175512167
- https://www.gendigital.com/us/en/contact-us/security-advisories/
- https://x.com/msnightmare2000/status/2094106041046765752
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.