Elusive Thoughts

External Service Interaction & Out-of-Band Resource Loads — Updated 2026 External Service Interaction & Out-of-Band Resource Loads Host Header Exploitation // SSRF Primitives // Infrastructure Pivoting SSRF Host Header Injection CWE-918 OWASP A10:2021 Cache Poisoning Updated 2026 In the recent past we encountered two relatively new types of attacks: External Service Interaction (ESI) and Out-of-Band Resource Loads (OfBRL). An ESI [1] occurs only when a web application allows interaction with an arbitrary external service. OfBRL [6] arises when it is possible to induce an application to fetch content from an arbitrary external location, and incorporate that content into the application's own response(s). Taxonomy Note (2026): Both ESI and OfBRL are now classified under OWASP A10:2021 — SSRF and map to CWE-918 (Server-Side Request Forgery). ESI also maps to CWE-441 (Unintentional Pro...

Intro This article is about basic types of port scanning. Port States (taking from Nmap man page) open An application is actively accepting TCP connections, UDP datagrams or SCTP associations on this port. closed A closed port is accessible (it receives and responds to Nmap probe packets), but there is no application listening on it. They can be helpful in showing that a host is up on an IP address (host discovery, or ping scanning), and as part of OS detection. Because closed ports are reachable, it may be worth scanning later in case some open up. Administrators may want to consider blocking such ports with a firewall. Then they would appear in the filtered state, discussed next. filtered Nmap cannot determine whether the port is open because packet filtering prevents its probes from reaching the port. The filtering could be from a dedicated firewall device, router rules, or host-based firewall software. Sometimes they respond with ICMP error messages such as type 3 c...