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This bulletin was written by Vigil@nce : http://vigilance.fr/

SYNTHESIS OF THE VULNERABILITY

When the administrator generated Legacy Certificates with OpenSSH
5.6/5.7, the Nonce field contains 32 bytes from the memory of the
ssh-keygen process.

Severity: 1/4

Creation date: 04/02/2011

IMPACTED PRODUCTS

– OpenSSH

DESCRIPTION OF THE VULNERABILITY

The ssh-keygen tool of OpenSSH generates certificates. Its "-t"
parameter indicates the type to generate:

- ssh-rsa-cert-v00@openssh.com : KEY_RSA_CERT_V00 (Legacy)

– ssh-dss-cert-v00@openssh.com : KEY_RSA_CERT_V00 (Legacy)

- ssh-rsa-cert-v01@openssh.com : KEY_RSA_CERT (current)

- ssh-dss-cert-v01@openssh.com : KEY_RSA_CERT (current)

Depending on the type (current/Legacy), the Nonce (random of 32
bytes) is located at the beginning/end of the message. However
when the Nonce has to be placed at the end of the message (Legacy
format), the key_certify() function of OpenSSH 5.6/5.7 does not
initialize it.

This error has to impacts:

- the Nonce contains data coming from the memory

- the Nonce may be predicted (low risk)

When the administrator generated Legacy Certificates with OpenSSH
5.6/5.7, the Nonce field therefore contains 32 bytes from the
memory of the ssh-keygen process.

ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN

http://vigilance.fr/vulnerability/OpenSSH-information-disclosure-via-Legacy-Certificates-10326