Protocol Downgrade Detector

Detect SSL/TLS protocol downgrade risks

About Protocol Downgrade Detector

Our free Protocol Downgrade Detector checks your TLS server for downgrade attack vulnerabilities including POODLE, TLS_FALLBACK_SCSV bypass, and version rollback attacks. Ensures your server enforces minimum TLS version requirements and is protected against downgrade attempts.

How to Use

Enter the domain name of the server to test for downgrade vulnerabilities
Click "Run" to perform the protocol downgrade detection scan
Review results to identify any downgrade attack vectors

Use Cases

•Downgrade attack prevention for critical web services
•PCI DSS compliance verification for TLS configuration
•Security hardening of legacy servers still supporting older protocols

Frequently Asked Questions

A protocol downgrade attack forces a TLS connection to use a weaker, earlier version of the protocol that has known vulnerabilities. Attackers intercept the initial handshake and trick both client and server into negotiating the lowest common protocol version.

TLS_FALLBACK_SCSV is a signaling cipher suite value that tells the server the client attempted a higher protocol version but fell back. If the server receives this signal but could have supported the higher version, it aborts the connection, preventing downgrade attacks.

POODLE (Padding Oracle On Downgraded Legacy Encryption) is a man-in-the-middle attack that exploits SSL 3.0's weak CBC cipher padding. The fix is to completely disable SSL 3.0 on your server, which no modern browser or client requires.

A server that still completes handshakes restricted to SSLv3, TLS 1.0 or TLS 1.1. Those versions have known design weaknesses, and every one a server accepts is a version an attacker can try to force a client down to. The grading is deliberately coarse — none, one, or several weak versions — because the remediation is the same regardless: stop offering them.

Because a single normal handshake only reveals the best version both ends support, which hides everything weaker the server would also accept. Pinning the probe to one version at a time asks the question a real handshake never asks: do you still speak this old version? Only separate attempts produce the per-version table the risk grade is built from.

Preference and acceptance are different things. A server can prefer 1.3 for modern clients while still completing a 1.0 handshake for anything that asks — and attackers ask. The risk finding reports acceptance, which is what matters for downgrade attacks. The fix is disabling the old versions server-side, not merely preferring the new ones.

On forgotten infrastructure, yes: old load balancers, embedded devices and long-untouched virtual hosts. Finding SSLv3 accepted is the highest-risk outcome on this page because its flaws are practical, not theoretical. If this probe reports it, treat the result as an incident for that endpoint and disable the version before doing anything else.

Re-run this exact check after changing the configuration and reloading. Each disabled version should flip from supported to unsupported in the per-version lines, and the risk grade should fall to none. If a version still shows as supported, the change did not reach the serving path — a second TLS terminator in front, such as a CDN or proxy, is the usual explanation.

How the Downgrade Test Works

This page attempts five separate handshakes with the server, each pinned to exactly one protocol version from SSLv3 through TLS 1.3. A version counts as supported only when a handshake restricted to it completes — the most direct possible test of what the server accepts.

1Offer each version alone. Pinning both the minimum and maximum to one version forces the question per version: can you talk exactly this? A server that merely prefers modern versions but still accepts old ones answers yes to the old ones too.
2Record five yes-or-no outcomes, one per version, reported as a simple supported-or-not line each. There is no inference and no banner parsing — completed handshake means supported, failed handshake means not.
3Grade the downgrade risk from the weak tail: none of SSLv3, TLS 1.0 or 1.1 means no risk, one of them means low, two or more means high. The grade follows directly from the measured outcomes.

This is the page that justifies disabling old versions, because it shows them actually negotiable rather than theoretically enabled. Re-run it after hardening to confirm each old version now fails — the before-and-after pair is the evidence the change worked.

Tips & Best Practices

•Test protocol downgrade attack resistance on your servers
•Enable TLS_FALLBACK_SCSV for downgrade protection
•Disable deprecated protocols to prevent downgrade attacks
•Monitor for downgrade attack attempts in server logs

Technical Details

Attack: Protocol downgrade attack detection and prevention
Protection: TLS_FALLBACK_SCSV and protocol configuration
Testing: Downgrade attack simulation
Output: Downgrade protection status and recommendations

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