Heimdal is one of the most widely-used open-source implementations of Kerberos—a protocol trusted for secure authentication in business, academic, and government networks. But in late 2022, a serious security flaw was found in its handling of PKI certificates. Known as CVE-2022-41916, this vulnerability could let attackers crash your critical authentication services, exposing your network to denial of service (DoS) attacks.

This guide gives a clear, jargon-free explanation of this vulnerability: what it is, how it works, how it could be exploited, and most importantly, how to patch your systems.

What is CVE-2022-41916?

CVE-2022-41916 is a denial of service vulnerability in Heimdal’s certificate validation code (specifically its libhx509 library). If a specially-crafted or rogue PKI certificate is received and parsed by Heimdal's KDC (Kerberos Key Distribution Center) or related tools (like kinit), Heimdal could crash, resulting in a denial of service.

Both PKINIT (Kerberos Public Key Cryptography for Initial Authentication) in the KDC and the client-side kinit command are affected. Third-party apps using Heimdal's libhx509 for certificate work are vulnerable as well.

Vulnerable versions: Heimdal versions before 7.7.1  
Fixed in: 7.7.1 and 7.8  
There are no known mitigations or workarounds—you have to upgrade.

Who’s at Risk?

If your network uses Heimdal for Kerberos authentication—with or without PKINIT—your KDC and clients may be vulnerable. This means:

Any application or script calling libhx509 for certificate validation

If your production or critical infrastructure depends on uninterrupted authentication, this flaw is especially dangerous. Crashing your KDC effectively cuts off user logins and network access.

How Does the Vulnerability Work?

At its heart, CVE-2022-41916 is a bug in DER/ASN.1 certificate parsing. The attacker crafts a malicious X.509 certificate, which when parsed by Heimdal's libhx509, triggers a crash—denying service for everyone.

Key technical details

- The bug is in how Heimdal validates certain certificate extensions, not checking memory bounds properly.
- Trigger can happen through PKINIT (in both KDC and client), or via remote requests using malicious certificates.

Example Code That Might Crash

While a full exploit is beyond scope here, the logic is simple: if your service parses (even just for checking) a malicious certificate like below, it may crash.

#include <hx509.h>

// Load a maliciously-crafted certificate
int main() {
    hx509_context ctx;
    hx509_cert cert;
    hx509_validate_ctx validate_ctx;

    hx509_context_init(&ctx);
    hx509_validate_ctx_init(ctx, &validate_ctx, );

    // 'bad_cert.der' is a DER file exploiting the bug
    if (hx509_cert_init(ctx, "FILE:bad_cert.der", NULL, NULL, &cert) == ) {
        hx509_validate_cert(ctx, validate_ctx, cert);
    }

    hx509_validate_ctx_free(&validate_ctx);
    hx509_cert_free(cert);
    hx509_context_free(&ctx);

    return ;
}

Given a dangerous certificate, this small program (or a KDC, or kinit, or any tool using the library) could segfault or crash—instantly denying authentication to real users.


## Potential Exploit/Attack Scenario

1. Attacker crafts and sends a malicious certificate, for example via a Kerberos PKINIT authentication request or by submitting it to an endpoint using Heimdal’s HX509.

No Workaround: Why You Must Patch

No sysctl, config change, or firewall tweak can mitigate this. It’s a parsing bug right where critical code needs to process certificates.

- If in doubt, check what version you’re running

kinit --version

Or in C code

printf("Heimdal version: %s\n", heimdal_version);

Use your distro’s package manager to update Heimdal (look for at least 7.7.1 or 7.8)

- If building from source, download the newest release from https://www.h5l.org/download.html and install

References

- Original CVE report: CVE-2022-41916
- Heimdal Security Advisory
- Heimdal Kerberos Project
- PKINIT documentation

TL;DR

If you use Heimdal Kerberos (directly or via another app):  
Patch now!  
A simple malicious certificate can knock your authentication offline, and there are no other fixes.

Staying up-to-date is the only way to keep your network and users safe.

Timeline

Published on: 11/15/2022 23:15:00 UTC
Last modified on: 02/16/2023 14:15:00 UTC