TLS renegotiation allows a client and server to renegotiate cryptographic parameters within an established TLS session. Secure renegotiation (RFC 5746) fixes a serious vulnerability where an attacker could inject their own traffic into a TLS session through a man-in-the-middle attack. Our checker tests whether your server supports secure renegotiation and whether it is vulnerable to insecure renegotiation attacks.
How to Use
Enter the domain name of the server you want to test.
Click "Check" to test the server's TLS renegotiation support.
Review the results showing secure renegotiation support, insecure renegotiation status, and RFC 5746 compliance.
If insecure renegotiation is detected, update your server configuration immediately.
Use Cases
•Verify that servers are patched against the TLS renegotiation MITM vulnerability
•Check RFC 5746 compliance for security audits and penetration tests
•Identify legacy servers that may still support insecure renegotiation
•Validate security configuration after server updates and patches
Frequently Asked Questions
TLS renegotiation is a mechanism that allows a client and server to renegotiate cryptographic parameters within an existing TLS session. It can be initiated by either party and is used for purposes like updating encryption keys or requesting client certificates mid-session.
Discovered in 2009, the TLS renegotiation vulnerability allowed an attacker to inject arbitrary data into a TLS session by performing a man-in-the-middle attack during renegotiation. RFC 5746 fixed this by adding cryptographically binding the renegotiation handshake to the original connection.
To fix insecure renegotiation, update your server software to the latest version. Most modern web servers (Apache, Nginx, IIS) have been patched since 2010. Ensure you are running a supported version with all security updates applied. For OpenSSL-based servers, version 0.9.8m or later includes the fix.
Not deliberately. Secure renegotiation is a fix for flaws in the original mechanism, and the correct modern position is to use TLS 1.3, where renegotiation was removed entirely rather than repaired. If you must support 1.2 for older clients, ensure secure renegotiation is active there, because its absence is what makes the downgrade attack practical — but treat it as legacy compatibility, not a feature to seek out.
Because TLS 1.3 deleted renegotiation from the protocol. It existed to let a client renegotiate within an existing connection, mostly so a server could ask for a stronger cipher, and with 1.3's simpler handshake there is nothing to renegotiate. A 1.3 server therefore cannot be vulnerable to the attacks renegotiation enabled, which makes it the strongest possible answer on this page.
An attack where an active network attacker forces clients and servers onto TLS 1.2 instead of 1.3 by tampering with the handshake, then exploits a vulnerability in 1.2 — a weak cipher or a missing integrity check on the Finished message — to decrypt traffic. Secure renegotiation is what prevents the downgrade, because it makes the handshake tamper-evident. This is a main reason 1.3 is worth enabling.
No, and it does not try to. The renegotiation_info extension is not exposed through this client library, so support cannot be determined from a handshake probe. The page reports the negotiated version and what that implies, then tells you to verify in the server configuration. Claiming a verdict here would be asserting a measurement nobody made.
It depends entirely on your protocol version. On TLS 1.3 it is correct and irrelevant. On 1.2 it would be a genuine problem if confirmed, since it enables the downgrade attack — so check the configuration directly before acting. And if your clients can all handle 1.3, the better response is to enable 1.3 and stop running the old protocol at all.
What Is Reported
Renegotiation was a client-initiated second handshake within an existing connection. It is a legacy mechanism with a specific history of serious flaws, and what matters today is whether your protocol version is one where the issue still exists.
1On TLS 1.3, report that renegotiation does not exist. The protocol removed it entirely, so a 1.3 server neither supports it nor is exposed to the attacks it enabled. That is a better outcome than a pass, and the page says so rather than reporting support.
2On 1.2 and below, report that it is not determinable here, because the renegotiation_info extension is not observable through this client library. Absence of secure renegotiation on 1.2 is a real finding — it is what enables the TLS 1.2 downgrade attack.
3Never claim support without evidence. An earlier version returned support as a constant on any successful connection, which would have reported a TLS 1.3 server as supporting a feature the protocol deleted.
The practical remediation is not about enabling renegotiation — it is about not running 1.2 without secure renegotiation if you must support it, and otherwise moving to 1.3 where the whole question disappears.
Tips & Best Practices
•Configure TLS renegotiation securely to prevent renegotiation attacks
•Use secure renegotiation (RFC 5746) for all TLS connections
•Monitor renegotiation usage for security awareness
•Disable renegotiation if not required for your application
Technical Details
Protocol: TLS renegotiation support and security analysis Secure: RFC 5746 secure renegotiation implementation Risk: Renegotiation attack vulnerability assessment Output: Renegotiation support status with security recommendations
