# CVE-2026-127029: Freeradius: stack-based buffer overflow via unbounded eap-sim identity length

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

A flaw was found in freeradius's Extensible Authentication Protocol Method for Subscriber Identity Module (EAP-SIM) module. When handling authentication requests, the server copies a client-supplied identity into an internal structure without properly checking its length against a fixed-size buffer. An unauthenticated remote attacker can exploit this issue by sending specially crafted EAP-SIM messages, triggering a stack buffer overflow that crashes the service and results in a Denial of Service (DoS).

## Remediation

- workaround: Disable the EAP-SIM submodule in the FreeRADIUS configuration if SIM-based authentication is not required:

1. Edit `/etc/raddb/mods-available/eap` (or `/etc/raddb/mods-enabled/eap`) and comment out or remove the `sim` configuration block within the `eap` module definition:

```
# sim {
# }
```

2. Restart the FreeRADIUS service to apply the changes:

```
systemctl restart radiusd
```

Warning: Restarting or reloading the FreeRADIUS service will temporarily interrupt active RADIUS authentication requests. Clients relying on EAP-SIM authentication will no longer be able to authenticate.

Additionally, restrict RADIUS UDP traffic (ports 1812 and 1813) to trusted Network Access Server (NAS) IP addresses using firewall rules to limit exposure to untrusted networks. (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-2026-127029 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2572339 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

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

- https://github.com/FreeRADIUS/freeradius-server/commit/e415f818dcdf91626e5e7314b3a4f819ab11f572 (CNA: redhat)

- https://access.redhat.com/security/cve/CVE-2026-127029 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2572339 (secalert@redhat.com)

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

- https://github.com/FreeRADIUS/freeradius-server/commit/e415f818dcdf91626e5e7314b3a4f819ab11f572 (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-127029; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-127029; retrieved 2026-11-12; source updated 2026-11-12

Revision: 091b64155e7125fa31db37663234b9b66b3f0d70cd5bf4a6b45229c029743ab9

Canonical: https://y2.dev/cve/CVE-2026-127029

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