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**Affected builds:** NG FCS, NG FP1, NG FP2, NG FP3 HF2, and NG with Application Intelligence R54/R55.
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**Requirement:** The HTTP Security Server or AI HTTP proxy must be enabled and transparently inspecting the targeted port; if HTTP inspection is disabled the vulnerable code path is never reached.
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{{#include ../banners/hacktricks-training.md}}
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### Triggering the error handler
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The proxy rejects malformed HTTP messages and builds its own error page with `sprintf(errbuf, attacker_string);`, letting attacker-controlled bytes act as the format string. Send an invalid request through the firewall and look for a proxy-generated error that reflects your payload:
If HTTP inspection is active, the firewall (not the backend server) answers immediately, proving the middlebox parsed and replayed the request line.
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### Exploitation
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#### Format string primitive
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- Force the parser into the error routine (invalid method, URI, or headers).
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- Place attacker-controlled dwords up front so `%x`, `%s`, and `%n` directives treat them as stack arguments.
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- Use `%x/%s` to leak pointers, then `%n/%hn` to write the formatted byte count into chosen addresses, overwriting return pointers, vtables, or heap metadata before hijacking execution with injected shellcode or ROP.
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#### Heap overflow primitive
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The same unsafe `sprintf()` writes into a fixed-size heap buffer. Mix a long request body with oversized directives (e.g., `%99999x`) so the formatted output overruns the allocation and corrupts adjacent heap structures, letting you forge freelist pointers or function tables that are later dereferenced.
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### Impact
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Compromise of the proxy grants code execution inside the firewall process (SYSTEM on Windows appliances, root on UNIX), enabling rule manipulation, traffic interception, and pivoting deeper into the management network.
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