CVE-2024-22532

Executive Summary

CVE-2024-22532 identifies a buffer overflow vulnerability in XNSoft NConvert version 7.163 for Windows x86. The flaw is triggered when processing a crafted XWD (X Window Dump) file, leading to a denial of service (DoS) condition. The vulnerability resides in the image parsing routine, where insufficient bounds checking allows an attacker to overflow a stack buffer. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild.

Supply Chain & Package Security

This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. It is a standalone Windows binary application.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the nature of the vulnerability (buffer overflow leading to DoS), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – requires user to open a malicious file.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – victim must open the file.
• Scope (S): Unchanged (U) – vulnerability does not cross trust boundaries.
• Confidentiality (C): None (N) – no data leak.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – application crash.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium – Exploitation requires user interaction and results only in DoS, but no patch exists.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the XWD file parser of NConvert. XWD files contain a header with image dimensions (width, height) and pixel data. The parser likely allocates a fixed-size stack buffer for pixel processing. By providing a crafted XWD file with a width or height value that exceeds the expected maximum, the parser copies pixel data beyond the buffer boundary, overwriting the return address or other critical stack data.

Root Cause: Lack of input validation on image dimensions before memory copy operations.

Attack Vector: An attacker sends a malicious XWD file to a victim via email, download, or other means. When the victim opens the file with NConvert, the overflow triggers a crash (DoS). In theory, with precise control over the overflow data, code execution could be possible, but no public exploit confirms this.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the XWD parsing routine of NConvert 7.163. A hypothetical fix would involve:

• Vulnerable: memcpy(buffer, pixel_data, width * height * bytes_per_pixel); without checking if width * height * bytes_per_pixel exceeds buffer_size.
• Patched: Adding a bounds check: if (width * height * bytes_per_pixel > buffer_size) { return error; } and using safe functions like memcpy_s.

Exploitation & Lab Setup

Red Team

No public exploit code exists. To develop a proof-of-concept, an attacker would:

1. Fuzz NConvert with malformed XWD files to identify the exact offset to overwrite EIP.
2. Craft a malicious XWD file with a crafted width/height field (e.g., 0xFFFFFFFF) to cause a large memory copy.
3. Test locally by running nconvert.exe -o output.png malicious.xwd.

Example XWD file structure (hex):

00000000: 4E 4F 52 4D 41 4C 00 00 00 00 00 00 00 00 00 00  (header)
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
...
00000040: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00  (width = 0xFFFFFFFF)
00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
...

The overflow occurs when the parser reads the width and copies pixel data.

Blue Team

• Monitor for crashes of nconvert.exe in Windows Event Logs (Event ID 1000).
• Deploy file reputation rules to block XWD files from untrusted sources.
• Use AppLocker to restrict execution of NConvert to trusted users only.
• Enable ASLR and DEP on the system to mitigate potential code execution.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): None available (no known malicious samples).
• File Type: .xwd files with anomalous header values (e.g., width > 65535).
• Process: nconvert.exe crashing with exception code 0xc0000005 (access violation).
• Network: No network indicators – local file-based attack.

Detection Engineering

YARA Rule

rule CVE_2024_22532_XWD_Overflow {
    meta:
        description = "Detects malicious XWD files targeting NConvert buffer overflow"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-22532"
    strings:
        $xwd_header = "NORMAL" ascii wide
        $large_width = { FF FF FF FF } // width = 0xFFFFFFFF
    condition:
        $xwd_header at 0 and $large_width at 0x40
}

Sigma Rule

title: NConvert XWD Buffer Overflow Crash
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects crashes of nconvert.exe due to malicious XWD file
author: Valters IT
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        Image: '*\\nconvert.exe'
        ExceptionCode: '0xc0000005'
    condition: selection
falsepositives:
    - Legitimate crashes due to corrupted files
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-22532 - Malicious XWD file download"; flow:to_client; file.name:/\.xwd$/i; file.size:>1000000; content:"NORMAL"; offset:0; content:"|FF FF FF FF|"; distance:64; within:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• No patch available – consider removing or replacing NConvert with an alternative image converter (e.g., ImageMagick, IrfanView).
• Restrict file types – block .xwd files at email gateways and web proxies.
• User education – warn users not to open XWD files from untrusted sources.
• Monitor for crashes and investigate any suspicious XWD files.

Valters IT
Securing digital frontiers with precision.