CVE-2026-127030
Description
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).
Statement
This vulnerability is rated as an Important severity because an unauthenticated remote attacker can crash the FreeRADIUS service, causing a complete denial of service prior to credential validation. In typical Red Hat Enterprise Linux deployments, EAP-FAST is an optional authentication method that is not enabled by default. Consequently, only environments that have explicitly configured and enabled the EAP-FAST submodule are exposed to this vulnerability.
Mitigation
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.
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)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Acknowledgements
Red Hat would like to thank s4cr00t (Alipay Security Team) for reporting this issue. Upstream acknowledges Ada Logics and TristanInSec@gmail.com as the original reporters.
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