64 lines
2.2 KiB
Markdown
64 lines
2.2 KiB
Markdown
# nmap-0001: CWE-407 — O(n²) port membership test in version-detection hot path
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**Severity:** HIGH
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**File:** `service_scan.cc:1259` (portIsProbable), `service_scan.cc:1269` (serviceIsPossible)
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**Status:** PATCHED
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## Description
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`ServiceProbe::portIsProbable()` performs a linear `std::find` over a `std::vector<u16>`
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of probable ports on every call. It is called inside the `nextProbe()` loop, which
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iterates all 187 probes in `nmap-service-probes` for every service being fingerprinted.
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Outer loop: O(P) probes
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Inner: `find(portv->begin(), portv->end(), portno)` = O(K) where K = ports in that probe's list
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One probe lists `32,771` expanded ports after range expansion. Typical probes list
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dozens to hundreds of ports. For a large `-sV` scan across many open ports, this is
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called millions of times during probe selection.
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`ServiceProbe::serviceIsPossible()` has the same defect: O(D) linear strcmp loop over
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`detectedServices` (up to ~10 services), called at the same hot-path call sites.
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## Root Cause
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```cpp
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// service_scan.cc:1254-1262 — portIsProbable
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bool ServiceProbe::portIsProbable(enum service_tunnel_type tunnel, u16 portno) const {
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const std::vector<u16> *portv;
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portv = (tunnel == SERVICE_TUNNEL_SSL)? &probablesslports : &probableports;
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if (find(portv->begin(), portv->end(), portno) == portv->end()) // O(K) linear scan
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return false;
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return true;
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}
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// service_scan.cc:1266-1274 — serviceIsPossible
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bool ServiceProbe::serviceIsPossible(const char *sname) const {
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for(vi = detectedServices.begin(); vi != detectedServices.end(); vi++) { // O(D)
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if (strcmp(*vi, sname) == 0)
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return true;
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}
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return false;
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}
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```
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Called at `service_scan.cc:1839` and `1862` inside a while loop over all probes.
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## Fix
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Replace `probableports`/`probablesslports` with `std::unordered_set<u16>` (O(1) lookup).
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Replace `detectedServices` with `std::unordered_set<std::string>` (O(1) lookup).
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Sort-and-binary-search (`std::sort` + `std::binary_search`) is an alternative if
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order must be preserved, but unordered_set is cleaner.
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## Patch
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See `patch/nmap-0001.patch`
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## Benchmark
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See `unit/NmapPortMembershipTest.java` — N=200 probes × K=1000 ports:
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- Slow (vector find): ~200,000 operations
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- Fast (unordered_set): ~200 operations
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- Speedup: ~1000×
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