CVE-2025-9033 Overview
CVE-2025-9033 is a heap buffer out-of-bounds read vulnerability in the Avira Antivirus engine. The flaw triggers when the engine scans a malformed PDF file. Successful exploitation can lead to local code execution or denial-of-service of the antivirus engine process.
The vulnerability affects Avira Antivirus on Windows, macOS, and Linux for engine builds prior to 8.3.70.76. Because antivirus engines automatically scan files placed on disk, attackers can stage a malicious PDF and rely on automatic scanning to reach the vulnerable parser.
Critical Impact
A malformed PDF processed by the Avira scanning engine can crash the antivirus process or enable local code execution within its context, undermining the security tool itself.
Affected Products
- Avira Antivirus on Windows (engine builds before 8.3.70.76)
- Avira Antivirus on macOS (engine builds before 8.3.70.76)
- Avira Antivirus on Linux (engine builds before 8.3.70.76)
Discovery Timeline
- 2026-06-12 - CVE-2025-9033 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-9033
Vulnerability Analysis
The issue is a heap-based out-of-bounds read classified under [CWE-125]. The Avira engine parses PDF documents during signature and heuristic scanning. When a crafted PDF contains malformed structures, the parser reads beyond the allocated heap buffer.
Reading outside the buffer can expose adjacent heap memory or reference unmapped pages. The first outcome leaks data that may be useful for further exploitation. The second outcome terminates the scanning process, producing a denial-of-service condition against the antivirus engine.
The advisory also indicates a path to local code execution. This typically occurs when the out-of-bounds value influences control flow, function pointer dereferences, or downstream memory operations within the parser.
Root Cause
The root cause is missing or incorrect bounds validation in the PDF parsing path of the Avira engine. The parser trusts length or offset fields embedded in the PDF and uses them without verifying that subsequent reads remain within the allocated heap allocation. Malformed PDF objects therefore drive the read pointer past the buffer boundary.
Attack Vector
Exploitation requires the malicious PDF to be processed by the engine on the target host. An attacker delivers the file through email, web download, network share, or a USB device. User interaction is required to place the file where Avira scans it, but on-access scanning then triggers the parser automatically.
Because the antivirus engine commonly runs with elevated privileges, code execution within the engine process grants meaningful local impact. See the Gen Digital Security Advisory for vendor details.
No public proof-of-concept is available at this time, and the vulnerability is not listed in the CISA KEV catalog.
Detection Methods for CVE-2025-9033
Indicators of Compromise
- Unexpected termination or repeated crashes of the Avira scanning engine process on Windows, macOS, or Linux endpoints.
- PDF files written to commonly scanned paths that exhibit malformed object streams or invalid cross-reference tables.
- Avira engine versions reporting a build number lower than 8.3.70.76.
Detection Strategies
- Inventory Avira engine builds across the fleet and flag any host below 8.3.70.76 as exposed to CVE-2025-9033.
- Monitor application crash telemetry (Windows Event Log, macOS ReportCrash, Linux core dumps) for faults originating in Avira engine modules.
- Correlate antivirus engine crashes with recent file write events for PDF artifacts to identify suspicious scan triggers.
Monitoring Recommendations
- Alert on unscheduled restarts of the Avira service or engine processes, which can indicate denial-of-service attempts.
- Track file creation events for PDFs originating from external sources (email gateways, browser downloads, removable media).
- Forward antivirus engine telemetry to a centralized log platform to surface clusters of parser failures across endpoints.
How to Mitigate CVE-2025-9033
Immediate Actions Required
- Update the Avira Antivirus engine to build 8.3.70.76 or later on all Windows, macOS, and Linux hosts.
- Validate engine version after update by checking the Avira management console or local product UI.
- Restrict ingestion of untrusted PDF files until patched, especially on shared file servers scanned by Avira.
Patch Information
Gen Digital has released a fixed Avira Antivirus engine build 8.3.70.76 that addresses the out-of-bounds read in the PDF parser. Apply the update through normal Avira engine update channels. Refer to the Gen Digital Security Advisory for the authoritative fix guidance.
Workarounds
- Where immediate patching is not possible, block delivery of PDF attachments at the email gateway and web proxy.
- Disable on-access scanning of PDF files temporarily if operationally acceptable, accepting the trade-off in malware coverage.
- Isolate hosts that cannot be updated and limit their exposure to untrusted file sources.
# Configuration example: verify Avira engine build on Linux
/opt/avira/bin/savapi --version
# Ensure reported engine version is 8.3.70.76 or higher
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
