AvastSvc denial of service via unhandled JsonCpp exceptions in native message handlers

Overview

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.

Affected

• avast_antivirus_avast_one_avast_premium_security_avast_ultimate_avast_business_security < 26.7
• avg_antivirus_free_avg_internet_security_avg_ultimate < 26.7
• norton_antivirus_plus_norton_360_standard_norton_360_deluxe_norton_360_advanced < 26.7

Remediation

Gen Digital has released a fix in Avast, AVG, and Norton version 26.7 and later. The fix adds exception handlers around JSON type conversions in the native message dispatcher, catching and safely logging JsonCpp exceptions instead of allowing them to propagate and crash the service. The fix addresses all three vulnerable code paths simultaneously.

Upgrade to version 26.7 or later to remediate this issue.