CVE-2026-71200
Description
If a KDC is configured to allow PKINIT authentication, an unauthenticated attacker can trigger a null pointer dereference, causing the process to terminate.
Statement
This vulnerability is rated as Important because an unauthenticated remote attacker can crash the Kerberos Key Distribution Center (KDC) daemon, leading to a complete denial of service across the authentication realm. In default Red Hat Enterprise Linux configurations, PKINIT pre-authentication is not activated; exploitation strictly requires the administrator to have explicitly enabled PKINIT via pkinit_identity and pkinit_anchors in the KDC configuration. Deployments operating with standard Kerberos authentication mechanisms and without PKINIT configured are unaffected.
Mitigation
Disable PKINIT on the KDC if certificate-based authentication is not required, or restrict network access to the KDC service using firewall rules.
1. Disabling PKINIT:
Edit `/var/kerberos/krb5kdc/kdc.conf` and comment out or remove the `pkinit_identity` and `pkinit_anchors` directives within the realm configuration:
# pkinit_identity = FILE:/etc/krb5kdc/kdc.pem,/etc/krb5kdc/kdckey.pem
# pkinit_anchors = FILE:/etc/krb5kdc/cacert.pem
Apply the changes by restarting the service:
systemctl restart krb5kdc.service
2. Restricting Network Access:
If PKINIT cannot be disabled, restrict network access to port 88 (UDP/TCP) to trusted client subnets using firewalld:
firewall-cmd --permanent --zone=internal --add-service=kerberos
firewall-cmd --permanent --zone=internal --add-source=192.168.1.0/24
firewall-cmd --reload
Caveats:
Disabling PKINIT prevents users and services from using smart cards or X.509 certificate pre-authentication. Restricting network access prevents unlisted subnets from obtaining Kerberos tickets.
Warning: Restarting `krb5kdc.service` will cause a momentary interruption to active authentication requests.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
Acknowledgements
This issue was discovered by Ada Logics, Erin Liman, and Found by AISLE in partnership with Red Hat.
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