[gnutls-help] issue with Windows 2008r2 Ldap

Nikos Mavrogiannopoulos nmav at gnutls.org
Wed Dec 30 11:13:31 CET 2015

On Tue, Dec 29, 2015 at 7:51 PM, André Liechti <andre at liechti.net> wrote:
> Like other people, I had this issue, and I had to fix it as soon as possible.
> I dug a little bit, I put the Windows 2012R2 server in debug mode for Schannel (https://support.microsoft.com/en-us/kb/260729), and I tried to bind using ldaps, with the following errors:
> - An TLS 1.2 connection request was received from a remote client application, but none of the cipher suites supported by the client application are supported by the server. The SSL connection request has failed.
> - A fatal alert was generated and sent to the remote endpoint. This may result in termination of the connection. The TLS protocol defined fatal error code is 40. The Windows SChannel error state is 1205.
> Found on Microsoft forum:
> "When OpenSSL establishes the connection to AD LDAP it sends its client cipher list, but TLSv1.2 allows for a longer cipher list than earlier versions, AD LDAP doesn't seem to accept this. When the longer list gets sent AD believes its a corrupted packet so drops the connection." (https://social.technet.microsoft.com/Forums/windows/en-US/b6ffa278-4a04-4609-ac35-8390f5ba9cb6/ldap-over-ssl-on-windows-2012r2-server-dcs-tls-12-not-working?forum=winserversecurity)
> After disabling the TLS1.2 support, I was able to bind using ldaps:
> -An SSL server handshake completed successfully. The negotiated cryptographic parameters are as follows.
> - Protocol: TLS 1.1
> - CipherSuite: 0x2F
> - Exchange strength: 1024
> I don't know exactly which cipher suite has a problem, but currently it's enough for me to work with TLS 1.1.

That's interesting. As I understand it, it means that the client hello
is larger than some limit required by this server. Does disabling some
legacy ciphersuites has the same effect as disabling TLS 1.2? e.g. a
priority string such as

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