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.
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| MISP | MISP Modules | affected |
|
No data.
No data.
No data available yet.
Vendor Solution
The fix extends the BLOCKED_RANGES list in is_safe_url() to include the previously missing IP address ranges: 0.0.0.0/8, 100.64.0.0/10, ::/128, fc00::/7, and fe80::/10. The existing IPv4-mapped IPv6 normalisation logic ensures that mapped forms (e.g., ::ffff:0.0.0.0) are also blocked. Regression tests are added covering both literal IP addresses in URLs and hostnames that resolve to the newly blocked ranges.
Tracking
Sign in to view the affected projects.
No advisories yet.
Mon, 19 Oct 2026 22:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | MISP html_to_markdown Module SSRF via Incomplete IP Range Blocking in is_safe_url() | |
| First Time appeared |
Misp
Misp misp Modules \(html To Markdown Expansion Module\) |
|
| Weaknesses | CWE-20 CWE-918 |
|
| CPEs | cpe:2.3:a:misp:misp_modules_\(html_to_markdown_expansion_module\):*:*:*:*:*:*:*:* | |
| Vendors & Products |
Misp
Misp misp Modules \(html To Markdown Expansion Module\) |
|
| References |
| |
| Metrics |
cvssV4_0
|
MITRE
Status: PUBLISHED
Assigner: CIRCL
Published:
Updated: 2026-10-19T22:19:50.011Z
Reserved: 2026-10-19T22:19:44.187Z
Link: CVE-2026-112991
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.