MISP html_to_markdown Module SSRF via Incomplete IP Range Blocking in is_safe_url()
Summary
| CVE | CVE-2026-112991 |
|---|---|
| State | PUBLISHED |
| Assigner | CIRCL |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-19 23:17:36 UTC |
| Updated | 2026-10-20 07:17:09 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 6.3 MEDIUM from 5a6e4751-2f3f-4070-9419-94fb35b644e8
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Problem Types: CWE-20 | CWE-918 | CWE-918 CWE-918 Server-Side Request Forgery (SSRF) | CWE-20 CWE-20 Improper Input Validation
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 5a6e4751-2f3f-4070-9419-94fb35b644e8 | Secondary | 6.3 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 6.3 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N |
CVSS v4.0 Breakdown
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | MISP | Misp-modules | affected 3.0.12 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/misp/misp-modules/commit/98a1c2c2f297665dd8d4609e9cd644007a57... | 5a6e4751-2f3f-4070-9419-94fb35b644e8 | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: elhoim (en)
CNA: Claude Opus 5 (1M context) (en)
Additional Advisory Data
Solutions
CNA: 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.