# FormCms avatar upload feature has a stored cross-site scripting (XSS) vulnerability

Advisory record · `GHSA-4fxf-xgrm-8fcj`

- **Identifiers:** `GHSA-4fxf-xgrm-8fcj` · `CVE-2025-56236`
- **State:** Confirmed
- **Severity:** CVSS 6.1 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-79](https://cwe.mitre.org/data/definitions/79.html) · [CWE-434](https://cwe.mitre.org/data/definitions/434.html)
- **Tags:** [Cross-site scripting (XSS)](https://agentprime.io/advisories/tag/xss.md) · [Unrestricted file upload](https://agentprime.io/advisories/tag/file-upload.md)
- **Published:** 28 Aug 2025
- **Updated:** 28 Aug 2025
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 28 Aug 2025, 15:30 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `FormCMS` (NuGet): affected `<0.5.7`; fixed in `0.5.7`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> FormCMS versions before 0.5.7 are vulnerable to stored cross-site scripting through the avatar upload feature. An authenticated user can upload an HTML file containing malicious JavaScript, and when a privileged user opens the publicly accessible file, the script runs in that user's browser. Upgrade FormCMS to version 0.5.7 or later.

Written 9 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.1 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`, from ADP (CISA-ADP)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0020, the 10th percentile, on 11 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:22 UTC: First seen by agentprime
- 31 Oct 2026, 15:22 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-4fxf-xgrm-8fcj)

## Sources

- [GitHub Advisory Database: GHSA-4fxf-xgrm-8fcj](https://github.com/advisories/GHSA-4fxf-xgrm-8fcj)
- [OSV: GHSA-4fxf-xgrm-8fcj](https://osv.dev/vulnerability/GHSA-4fxf-xgrm-8fcj)
- <https://nvd.nist.gov/vuln/detail/CVE-2025-56236>
- <https://github.com/FormCms/FormCms/issues/27>
- <https://github.com/KKC73/me/blob/main/CVE-2025-56236/README.md>
- <https://github.com/formcms/formcms>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-4fxf-xgrm-8fcj>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-4fxf-xgrm-8fcj/>. Everything for agents: <https://agentprime.io/llms.txt>.