Don't report DROWN from TLS 1.0 and TLS 1.1 alone

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Bug and impact

check_drown() treated any host with two or more deprecated TLS versions as confirmed DROWN (CVE-2016-0800, CRITICAL, CVSS 9.8), which forced TLS grade F.

Python cannot negotiate SSLv2, and the only deprecated versions the analyzer can actually probe are TLS 1.0 and TLS 1.1. A typical legacy stack that still offers both therefore got a false CRITICAL on every TLS scan — including hosts that have never spoken SSLv2.

Trigger: scan any host that successfully handshakes TLS 1.0 and TLS 1.1 (very common). probe_protocols() puts both in deprecated; len(deprecated) >= 2 fired DROWN.

Root cause

The DROWN heuristic used len(deprecated) >= 2 as a stand-in for SSLv2 because SSLv2 cannot be tested from Python. TLS 1.0 + TLS 1.1 is not DROWN. DROWN requires SSLv2 on the host or a shared RSA key with an SSLv2 server.

Fix

Only emit the DROWN finding when SSLv2 is actually present in the deprecated list. TLS 1.0/1.1 remain MEDIUM deprecated-protocol findings and still grade D when both are present.

Validation

• python3 -m pytest test_tls.py test_hardening.py -q — 61 passed
• New tests cover: TLS 1.0+1.1 must not emit DROWN; SSLv2 still does; probe → check → grade path is D not F