Fox News has a credibility problem. Most critics of the cable news network will be well aware of that, but in this case the admission is coming from Fox News itself.

An internal research briefing obtained by the Daily Beast names four regular contributors to the network for peddling “disinformation”, particularly when it comes to the Ukraine scandal that led to Donald Trump’s impeachment.

Among those named in the lengthy document titled Ukraine, Disinformation, & the Trump Administration, put together by Fox News senior political affairs specialist Bryan S Murphy, are frequent guests Rudy Giuliani, John Solomon, Victoria Toensing and Joe diGenova.

Solomon, a disgraced former writer for the Hill and a regular guest of Sean Hannity’s, comes under particular scrutiny. “John Solomon played an indispensable role in the collection and domestic publication of elements of this disinformation campaign,” the document explains.

Much of Solomon’s “reporting” on Ukraine formed the basis of Giuliani and other Trump officials’ efforts to smear and oust the former US ambassador to Ukraine Marie Yovanovitch, a figure seen as standing in the way of the president and former Ukraine officials’ shadowy machinations in the country.

Among the allegations against Solomon noted are “non-disclosure of conflicts, use of unreliable sources, publishing false and misleading stories, misrepresentation of sources, and opaque coordination with involved parties”.

Elsewhere in the file obtained by the Beast are details of Giuliani and his back-channel dealings to investigate former vice-president Joe Biden and his son Hunter, as well as his connections to now indicted figures Lev Parnas and Igor Fruman. Giuliani has a “high susceptibility to disinformation”, Murphy writes.

The credibility of Toensing and diGenova, a married couple of hyperpartisan Trump loyalists who were secretly working for the indicted Ukrainian oligarch Dmytro Firtash during the period of their regular appearances on Fox News, is also called into question as they did not disclose that relationship.

“Notable are the roles of Joe diGenova and Victoria Toensing in spreading disinformation and their parroting of beneficial narratives while employed by Firtash,” it explains.

Hannity, the popular primetime host and Trump confidant, is also criticized for laundering the reputations and trumpeting the trustworthiness of the guests in question.

According to Media Matters, the four individuals have made 348 appearances on Fox News weekday programs since 2018. About 203 of them were on Hannity’s program alone.

In a statement from Fox News, Mitch Kweit, senior vice-president of the Brainroom, said the research briefing was “being taken out of context and politicized to damage the network”.

Kweit added: “The Ukraine briefing book is nothing more than a comprehensive chronological account of what every person involved in the Ukraine controversy was doing at any identifiable point in time, including tracking media appearances of major players who appeared on Fox News and in many other outlets.”