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Researchers turn Avast sandbox kernel bug into SYSTEM-level exploit

Researchers turn Avast sandbox kernel bug into SYSTEM-level exploit

New Capabilities

Double-fetch flaw in aswSnx.sys driver patched in version 25.3; Microsoft mitigation blocks the technique

Today: SAFA publishes Part 2 exploit chain

Overview

Updated 2 hours ago

SAFA researchers published the full exploit chain for CVE-2025-13032, a double-fetch bug in Avast's aswSnx.sys kernel driver. On an up-to-date Windows 11 system, a race condition becomes a controlled pool overflow, then an arbitrary kernel read/write, and finally a stolen SYSTEM token.

Avast patched the flaw in version 25.3. Microsoft's user-mode accessors, which re-verify user buffers at each kernel access, block this exact technique on newer Windows. The writeup landed a month after PrettyPrague, a separate Avast sandbox bug that dumps the SAM database — antivirus kernel drivers keep proving a rich privilege-escalation surface.

Why it matters

Antivirus kernel drivers run with SYSTEM privileges on practically every Windows machine; a single flaw hands local attackers full control.

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Key Indicators

SYSTEM
Privilege level achieved by exploit
Full local privilege escalation from a standard user to SYSTEM on Windows 11.
6
Kernel flaws disclosed in aswSnx.sys
Four heap overflows and two local denial-of-service bugs, all under CVE-2025-13032.
25.3
Minimum patched Avast version
Versions before 25.3 carry the flawed driver; updating closes the pool overflow.

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People Involved

Organizations Involved

Timeline

2025 September 2026

6 events Latest: Today
Tap a bar to jump to that date
  1. SAFA publishes Part 2 exploit chain

    Today Publication

    Part 2 walks the full chain from pool overflow to corrupted IORing object to stolen SYSTEM token.

  2. Gen Digital confirms PrettyPrague fix

    Statement

    Gen Digital tells SecurityWeek the prettyprague vulnerability has been fixed in updates.

  3. PrettyPrague LPE published

    Disclosure

    NightmareEclipse publishes a separate Avast sandbox exploit that dumps the SAM database.

  4. SAFA publishes Part 1

    Publication

    Part 1 details the double-fetch bug and how to reach Avast's sandbox attack surface.

  5. Avast ships version 25.3 patch

    Patch

    Avast releases version 25.3, closing the double-fetch flaw in the sandbox kernel driver.

  6. CVE-2025-13032 assigned

    Discovery

    SAFA Team finds six kernel flaws in Avast's aswSnx.sys sandbox driver.

Scenarios

1

Microsoft's user-mode accessors close the double-fetch class

Likely Resolves by Q2 2027

Discussed by: Microsoft documentation; SAFA Team noted the mitigation will prevent the technique

Microsoft's user-mode accessors re-check at each kernel access that user buffers live in userspace, closing the time-of-check/time-of-use window the exploit depends on. If enforced by default in a shipping Windows build, even unpatched vendors' drivers can't be exploited this way. SAFA's Part 2 writeup explicitly flags this mitigation as the reason the technique won't work on the latest kernels.

2

Shared driver code exposes AVG or Norton to the same flaw

Possible Resolves by End of 2027

Discussed by: SAFA Team (AVG shares driver code); Binary House blog (sibling-product speculation)

AVG Antivirus runs the same aswSnx.sys codebase as Avast, and Gen Digital's sibling products are speculated to share the surface. If the double-fetch flaw shipped in that code and wasn't patched in lockstep, the same exploit chain works against AVG. Confirmation requires a researcher testing the AVG build or a new CVE.

3

Avast hardening holds, no further kernel disclosures

Uncertain Resolves by End of 2027

Discussed by: Avast security team, vendor response

Version 25.3 and follow-up hardening close the disclosed flaws, and no new exploitable kernel bugs surface in aswSnx.sys within a year of the Part 2 publication. The incident closes as contained, with the disclosed chain patched and the technique blocked by the Windows mitigation.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

2016

Project Zero's antivirus research (2016)

Google Project Zero researcher Tavis Ormandy found critical, remotely exploitable vulnerabilities in multiple antivirus products, including flawed parsers in Avast, Kaspersky, and others. One Avast bug let a remote attacker take over a machine just by visiting a webpage.

Then

Vendors rushed emergency patches; several products were shown to be remotely exploitable.

Now

The research established that antivirus software massively expands the attack surface it claims to protect.

Why this matters now

Same vendor, same pattern: antivirus replaces the kernel's built-in defenses with its own privileged, buggy code.

2021

Dell dbutil.sys (CVE-2021-21551)

A signed Dell driver, dbutil.sys, shipped multiple privilege-escalation flaws including an arbitrary read/write primitive. Exploits appeared in the wild before Dell patched it. Microsoft later added the driver to its vulnerable-driver blocklist.

Then

Dell released a fix; Microsoft blocked the driver on protected systems.

Now

Reinforced that signed vendor kernel drivers are a trusted, persistent local-privilege-escalation vector.

Why this matters now

The Avast bug exploits the same trust model — a vendor-signed kernel driver with memory-corruption flaws.

2022-2023

RTCore64 and BYOVD campaigns (2022–2023)

Malware used a legitimate signed MSI driver, RTCore64, to gain kernel access in bring-your-own-vulnerable-driver attacks. Microsoft responded by expanding its vulnerable-driver blocklist and tightening driver-signing policies.

Then

Microsoft added the driver to its blocklist; several campaigns switched tactics.

Now

Highlighted how the kernel trust placed in third-party signed drivers is both a feature and a liability.

Why this matters now

Avast's sandbox driver carries the same kernel trust; a bug in it is as good as handing attackers the keys.

Sources

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