MISP Modules up to 3.0.12 html_to_markdown is_safe_url server-side request forgery

Summaryinfo

A vulnerability identified as problematic has been detected in MISP Modules up to 3.0.12. This vulnerability affects the function is_safe_url of the component html_to_markdown. This manipulation causes server-side request forgery. This vulnerability is tracked as CVE-2026-112991. The attack is possible to be carried out remotely. No exploit exists. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability was found in MISP Modules up to 3.0.12. It has been declared as problematic. Affected by this vulnerability is the function is_safe_url of the component html_to_markdown. The manipulation with an unknown input leads to a server-side request forgery vulnerability. The CWE definition for the vulnerability is CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. As an impact it is known to affect confidentiality. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-112991 since 10/20/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details are known, but no exploit is available.

Applying the patch 98a1c2c2f297665dd8d4609e9cd644007a57516b is able to eliminate this problem.

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Productinfo

Vendor

• MISP

Name

• Modules

Version

• 3.0.0
• 3.0.1
• 3.0.2
• 3.0.3
• 3.0.4
• 3.0.5
• 3.0.6
• 3.0.7
• 3.0.8
• 3.0.9
• 3.0.10
• 3.0.11
• 3.0.12

License

• open-source

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