Yes, this is true. Details of torture is written in an article on the website Amnesty.org titled, "End the horror in Syria's torture prisons." In this article it states that "Former prisoners speak of an endless cycle of beatings. Many of the people we spoke to said they had been beaten with plastic hose pipes, silicone bars and wooden sticks. Some had been scalded with hot water and burnt with cigarettes. Others were forced to stand in water and given electric shocks."
Additionally, in the same article it states that "As many as 13,000 people have been hanged to death in Saydnaya between September 2011 and December 2015." Mass executions are being held at this prison and the bodies are loaded onto trucks and buried in mass graves, which is a massive injustice to human rights.
https://www.amnesty.org/en/latest/campaigns/2016/08/syria-torture-prisons/