---
id: "CVE-2026-112991"
kind: "vulnerability"
aliases: ["CVE-2026-112991"]
title: "MISP Modules: html_to_markdown SSRF reaches internal address ranges"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["misp", "misp-modules", "package", "self-hosted", "threat-intel"]
not_affected_if: ["module-disabled", "trusted-users-only"]
published_at: "2026-10-19T23:17:36+00:00"
first_seen_at: "2026-10-23T21:57:19+00:00"
updated_at: "2026-10-25T04:01:43+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112991", "first_seen_at": "2026-10-23T21:57:19+00:00"}]
---

# MISP Modules: html_to_markdown SSRF reaches internal address ranges

The html_to_markdown expansion module in MISP Modules fetches user-supplied URLs server-side, but its is_safe_url() blocklist misses several ranges including 0.0.0.0/8, 100.64.0.0/10, ::/128, fc00::/7, fe80::/10 and IPv4-mapped IPv6 forms. An authenticated user who can create or modify attributes that trigger the module can make the MISP server request internal services and read the responses.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the MISP Modules version installed (`pip show misp-modules` or the container image tag) and compare it with the fixed release, which the sources do not name.
- Check whether the `html_to_markdown` expansion module is enabled in the MISP Modules configuration (unknown from sources).

## Fix

- Upgrade MISP Modules to a release that extends BLOCKED_RANGES in is_safe_url() (fixed version: unknown from sources).
- Until patched, disable the `html_to_markdown` expansion module or restrict who can create or modify attributes.

## Timeline

- 2026-10-23T21:57:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112991

## From the sources

The html_to_markdown expansion module in MISP Modules contains a server-side request forgery (SSRF) vulnerability in its is_safe_url() URL validation function. The BLOCKED_RANGES list used to reject unsafe destination addresses was incomplete, omitting several critical IP address ranges. Specifically, the following ranges were not blocked: 0.0.0.0/8 (unspecified, which routes to loopback on Linux), 100.64.0.0/10 (carrier-grade NAT per RFC 6598), ::/128 (IPv6 unspecified), fc00::/7 (IPv6 Unique Local Addresses), and fe80::/10 (IPv6 link-local). The existing list only covered IPv4 loopback (127.0.0.0/8), RFC 1918 private ranges, IPv4 link-local (169.254.0.0/16), and IPv6 loopback (::1/128).

An authenticated user with the ability to create or modify MISP attributes that trigger the html_to_markdown expansion module could supply URLs pointing to these unblocked internal address ranges. Because the module fetches the URL server-side to convert HTML content to Markdown, the request is made from the MISP server's network context. This allows an attacker to probe and read responses from internal services, carrier-grade NAT infrastructure, or link-local endpoints that would otherwise be unreachable from external networks. IPv4-mapped IPv6 forms (e.g., [::ffff:0.0.0.0]) also bypassed the existing checks.

The security impact is primarily confidentiality: an attacker can read data served by internal services reachable from the MISP server. The MISP instance itself is not compromised, but it is abused as a proxy to access otherwise restricted network resources.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_