The report recommended Sandrock, who resigned as German Football Association (DFB) general secretary in February, is fined and should perform social work.
Fifa has been investigating Sandrock and five others since March over the awarding of the 2006 World Cup.
Last week, Swiss prosecutors opened a criminal investigation into the case.
Ex-DFB president Wolfgang Niersbach and Germany legend Franz Beckenbauer, who headed the bid, were named by the Swiss prosecutors as two of four individuals suspected of fraud, criminal mismanagement, money laundering and misappropriation.
Sandrock was not one of those named.
However, in its report Fifa's ethics committee said Sandrock had violated its general rules governing conduct, loyalty and duty of disclosure, cooperation and reporting.
In November, tax authorities raided the DFB's headquarters after it emerged the federation had made a secret payment of 6.7m euros (£4.6m) to Fifa in 2005.
An internal audit failed to find any trace of the 6.7m euros in the DFB's tax documents. The DFB denies the claims.
German news weekly Der Spiegel had claimed the money had been used to set up a slush fund to buy votes in the 2006 World Cup bidding process.
Fifa's ethics body will investigate ex-German official Helmut Sandrock after a report alleged he broke conduct rules during Germany's 2006 World Cup bid.