# CVE-2026-127030: Freeradius: stack buffer overflow via unchecked eap-fast sessionticket length

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

A flaw was found in freeradius. An improper length validation in the EAP-FAST module allows a stack-based buffer overflow during session ticket processing. A remote, unauthenticated attacker can exploit this flaw by sending a specially crafted handshake request, causing the server process to crash and resulting in a Denial of Service (DoS).

## Remediation

- workaround: Disable the EAP-FAST submodule in the FreeRADIUS configuration, or restrict incoming RADIUS traffic to trusted network access points.

1. Disable EAP-FAST:
In `/etc/raddb/mods-available/eap` (or `/etc/raddb/eap.conf`), comment out the `fast` section within the `eap` configuration block and verify that `default_eap_type` is not set to `fast`.

2. Apply configuration changes:
```
systemctl restart radiusd
```

3. Limit network exposure:
Restrict UDP port 1812 to authorized Network Access Server (NAS) clients using firewalld:
```
firewall-cmd --permanent --zone=internal --add-source=<TRUSTED_IP_OR_SUBNET>
firewall-cmd --permanent --zone=internal --add-port=1812/udp
firewall-cmd --reload
```

Caveats:
Disabling EAP-FAST prevents authentication for any network clients that rely exclusively on EAP-FAST. Restricting firewall rules will block traffic from unlisted authenticator sources.

Warning:
Restarting or reloading the radiusd service will temporarily disrupt active RADIUS authentication processing. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (freeradius): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (freeradius): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (freeradius): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (freeradius:3.0/freeradius): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (freeradius): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: redhat

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-127030 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2572340 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://github.com/FreeRADIUS/freeradius-server/commit/064567a08f3b9d9b4863fab6060fafe296ac7de9 (CNA: redhat)

- https://github.com/FreeRADIUS/freeradius-server/commit/a5d09dad528d7a3a3c4c01158716ab85a12e09ef (CNA: redhat)

- https://access.redhat.com/security/cve/CVE-2026-127030 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2572340 (secalert@redhat.com)

- https://github.com/FreeRADIUS/freeradius-server/commit/064567a08f3b9d9b4863fab6060fafe296ac7de9 (secalert@redhat.com)

- https://github.com/FreeRADIUS/freeradius-server/commit/a5d09dad528d7a3a3c4c01158716ab85a12e09ef (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-127030; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-127030; retrieved 2026-11-12; source updated 2026-11-12

Revision: b6a673adebdb72cfbe3da85b3df2e29d7b120eacfd9598358f639a2425df3954

Canonical: https://y2.dev/cve/CVE-2026-127030

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