CVE-2026-6676: Avira Antivirus Engine RCE Vulnerability

CVE-2026-6676 Overview

CVE-2026-6676 is a heap buffer out-of-bounds write vulnerability [CWE-787] in the Avira Antivirus engine. The flaw is triggered when the engine scans a malformed POSIX tar archive. Successful exploitation can result in local code execution or denial-of-service of the antivirus engine process.

The issue affects Avira Antivirus on Windows, macOS, and Linux for engine builds before 8.3.27.12. Because antivirus engines typically run with elevated privileges and automatically scan untrusted files, the attack surface is broad despite the local attack vector.

Critical Impact
An attacker who places a crafted tar archive on a target system can corrupt heap memory in the Avira scanning engine, potentially executing code in the security product's context or disabling protection.

Affected Products

Avira Antivirus on Windows (engine builds before 8.3.27.12)
Avira Antivirus on macOS (engine builds before 8.3.27.12)
Avira Antivirus on Linux (engine builds before 8.3.27.12)

Discovery Timeline

2026-06-12 - CVE-2026-6676 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-6676

Vulnerability Analysis

The vulnerability is a heap-based out-of-bounds write within the Avira Antivirus engine's archive parser. When the engine attempts to scan a POSIX tar archive, malformed header fields cause the parser to write past the bounds of a heap-allocated buffer. The corruption occurs in the address space of the antivirus engine process, which generally executes with elevated privileges.

User interaction is required to trigger the scan, but this can be as routine as saving a file to a monitored directory. Because the engine performs on-access scanning, the malformed archive does not need to be explicitly opened by the user. The result is either crashing the engine (denial-of-service) or steering execution flow through controlled heap corruption.

Root Cause

The root cause is insufficient validation of size or offset fields within POSIX tar headers before the engine writes parsed data into a heap buffer. POSIX tar headers use fixed-width octal numeric fields for sizes and offsets, and malformed values are not bounds-checked against the destination buffer. This classifies the defect as CWE-787 (Out-of-bounds Write).

Attack Vector

The attack vector is local with required user interaction. An attacker delivers a crafted POSIX tar archive through email attachment, web download, removable media, or a network share. When the Avira engine scans the file, parsing of the malformed header triggers the heap corruption. No authentication is required because scanning occurs automatically against any file the engine evaluates.

No verified public proof-of-concept code is currently available for CVE-2026-6676. Refer to the Gen Digital Security Advisory for vendor technical details.

Detection Methods for CVE-2026-6676

Indicators of Compromise

Unexpected crashes or restarts of the Avira Antivirus engine process, particularly correlated with archive scanning activity.
Presence of malformed POSIX tar archives in user download directories, email attachments, or temporary scan paths.
Engine log entries referencing parser exceptions or aborted scans of tar archives.

Detection Strategies

Monitor process integrity of the Avira engine for abnormal terminations or memory access violations.
Inspect file telemetry for tar archives with anomalous header values (invalid octal size fields, oversized name fields).
Correlate archive scan events with subsequent child process creation under the antivirus service account.

Monitoring Recommendations

Enable verbose logging on the Avira engine and forward logs to a centralized SIEM for analysis.
Alert on antivirus engine crashes followed by suspicious process activity on the same host.
Track engine version inventory across endpoints to identify hosts still running builds before 8.3.27.12.

How to Mitigate CVE-2026-6676

Immediate Actions Required

Update the Avira Antivirus engine to build 8.3.27.12 or later on all Windows, macOS, and Linux systems.
Verify that engine auto-update mechanisms are functioning and have applied the fixed build.
Audit endpoints to confirm no instances of the vulnerable engine remain in production.

Patch Information

Gen Digital has addressed the vulnerability in Avira Antivirus engine build 8.3.27.12. Engine updates are typically delivered through the standard Avira update channel. Consult the Gen Digital Security Advisory for distribution details and confirmation of fixed builds.

Workarounds

Restrict scanning of untrusted archive sources by limiting download and email attachment policies until patching is complete.
Block or quarantine inbound tar archives at the email gateway and web proxy where business needs allow.
Limit local user ability to write archive files to directories monitored by on-access scanning.

bash

# Verify Avira engine version on Linux
avira --version

# Expected output should show engine build 8.3.27.12 or later
# Example: Engine: 8.3.27.12