Live › vulnerability › CVE-2026-112991
Go to dashboardThe 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 written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Teams running MISP with the MISP Modules service and the html_to_markdown expansion module enabled, where users can create or edit attributes that trigger it. The MISP server's network position determines what is reachable, so instances with internal services or cloud metadata endpoints on the same network matter most. Instances without the module enabled, or where only trusted administrators can edit attributes, can skip it.
No product ranges from the sources yet.
pip show misp-modules or the container image tag) and compare it with the fixed release, which the sources do not name.html_to_markdown expansion module is enabled in the MISP Modules configuration (unknown from sources).html_to_markdown expansion module or restrict who can create or modify attributes.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
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.
This page as .md · .json · in your agent: get_signal("CVE-2026-112991")
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