CVE-2024-6820 Overview
CVE-2024-6820 is an out-of-bounds write vulnerability in IrfanView, a widely used Windows image viewer. The flaw resides in the AWD file parser and stems from insufficient validation of user-supplied data during file processing. Attackers can trigger a write past the end of an allocated buffer, leading to arbitrary code execution in the context of the current process. Exploitation requires user interaction, such as opening a crafted AWD file or visiting a malicious page that delivers one. The issue was reported through the Zero Day Initiative as ZDI-CAN-23232 and published as advisory ZDI-24-972. It is classified under [CWE-787] Out-of-Bounds Write.
Critical Impact
Successful exploitation grants arbitrary code execution on the victim's machine with the privileges of the user running IrfanView.
Affected Products
- IrfanView 4.66 (x64)
- IrfanView on Windows platforms
- Installations processing AWD (Artweaver Document) image files
Discovery Timeline
- 2024-11-22 - CVE-2024-6820 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-6820
Vulnerability Analysis
The vulnerability affects IrfanView's parser for AWD image files. When the application processes a malformed AWD file, it fails to validate size or offset fields properly before writing data into a heap or stack buffer. The result is an out-of-bounds write [CWE-787] that corrupts adjacent memory. Attackers who control the file contents can shape the overwrite to hijack execution flow. The advisory tracked as ZDI-24-972 describes the flaw as a local attack requiring user interaction, matching the vector AV:L/UI:R.
Root Cause
The root cause is missing bounds checking on attacker-controlled fields inside the AWD file structure. IrfanView trusts length or index values embedded in the file when performing buffer copies. Because the parser does not verify that the destination buffer can hold the requested data, a crafted file drives a write beyond the allocated region.
Attack Vector
Exploitation requires a user to open a malicious AWD file in IrfanView or navigate to a page that triggers file handling. Once the file is parsed, the out-of-bounds write executes code as the current user. This vector is common for phishing chains that lure victims into opening seemingly benign image attachments. See the Zero Day Initiative Advisory ZDI-24-972 for additional detail.
No verified public proof-of-concept code is available. The exploitation flow follows the pattern documented by ZDI: a crafted AWD file with oversized or malformed size fields triggers the out-of-bounds write during parsing, enabling attacker-controlled memory corruption and subsequent code execution.
Detection Methods for CVE-2024-6820
Indicators of Compromise
- Unexpected AWD files delivered via email attachments, download links, or removable media.
- IrfanView process (i_view64.exe or i_view32.exe) spawning child processes such as cmd.exe, powershell.exe, or rundll32.exe.
- Crashes or anomalous memory access events in IrfanView logged by Windows Error Reporting.
Detection Strategies
- Monitor endpoint telemetry for IrfanView launching interpreters, script hosts, or shell processes shortly after file open events.
- Alert on AWD files originating from untrusted zones (Internet, email) being opened by IrfanView.
- Correlate image viewer crashes with subsequent outbound network connections that suggest post-exploitation activity.
Monitoring Recommendations
- Enable process creation logging (Sysmon Event ID 1) and file open auditing on workstations that have IrfanView installed.
- Track IrfanView version inventory to identify hosts still running versions at or below 4.66.
- Ingest endpoint and file telemetry into a centralized data lake to hunt for anomalous AWD file activity across the fleet.
How to Mitigate CVE-2024-6820
Immediate Actions Required
- Update IrfanView to the latest release published after the ZDI-24-972 advisory.
- Restrict opening AWD files from untrusted sources until patching is complete.
- Remove IrfanView from systems that do not require it, reducing the attack surface.
Patch Information
Refer to the Zero Day Initiative Advisory ZDI-24-972 and the IrfanView vendor site for the fixed build. Confirm the installed version is newer than 4.66 x64 before treating a host as remediated.
Workarounds
- Disassociate the .awd file extension from IrfanView so files do not open automatically on double-click.
- Block or quarantine inbound AWD files at the email gateway and web proxy.
- Apply application allowlisting to prevent IrfanView from spawning shell or scripting interpreters.
- Educate users to avoid opening image files received from untrusted senders.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
