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leonardo's avatar
leonardo
Icon for Nimbostratus rankNimbostratus
Jan 23, 2020

Problem ssl validation

hello, I have a problem with an ssl validator, in https://validator.w3.org/feed/

 

Ciphers: DEFAULT:!RSA

https://validator.w3.org/feed/ Error (Server returned [SSL: DH_KEY_TOO_SMALL] dh key too small (_ssl.c:727)

sslabs Calification B

 

 

removing :!RSA

 

Ciphers: DEFAULT:!LOW:!RC4:!MD5:!SHA1:!ADH:!DHE:!DES:!3DES:!EXP

https://validator.w3.org/feed/ ok

sslabs Calification F (sslab recommend removing RSA)

This server is vulnerable to the Return Of Bleichenbacher's Oracle Threat (ROBOT) vulnerability. Grade set to F. MORE INFO »

BIG-IP SSL vulnerability

 

 

version. BIG-IP 11.6.0 Build 5.0.429 Hotfix HF5

 

Any ideas, what may be happening?

 

thanks

BIG-IP
LTM
security
ssl

1 Reply

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  • Samir's avatar
    Samir
    Icon for MVP rankMVP
    Jan 25, 2020

    Client SSL profile may be vulnerable to an Bleichenbacher attack against RSA, which when exploited, may result in plaintext recovery of encrypted messages and/or a Man-in-the-middle (MiTM) attack, despite the attacker not having gained access to the server's private key itself, aka a ROBOT attack. Inorder to correct you need to disable !RSA algorithm from cipher list.

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    It will help you to increase the ssl rating. I would suggest to add below cipher in client ssl profile( try in non prod application)

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    DEFAULT:ECDHE:!RSA:!DHE:!3DES

    Hope it will help you.

    Referenc link ​https://support.f5.com/csp/article/K21905460

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