Us Weekly is quoting several sources who say Glanville, 40, cheated on Cibrian, 39, several times during their eight-year marriage.
"Brandi loves to play the victim, but she doesn't tell the whole story," the magazine said, quoting one source.
Glanville, one of the stars of "Real Housewives of Beverly Hills" and author of a new book "Drinking & Tweeting," took to Twitter Tuesday to deny the report.
"Apparently I cheated on eddie a few times with some Hot guys!Wow!Grasping at straws 4 yrs later a week before book is out #WISHIHAD watev," she wrote.
She also referred directly to one of the allegations in the report that she had sex with another man weeks after giving birth to her second son.
"I had the baby blues after Jake was born I wasn't even hav n sex with EC let alone anyone else," she wrote. "Such BS but I kind of want to buy the mag now."
Country star Rimes, 30, had a very public affair with actor Cibrian while he was married to Glanville, and Rimes and Cibrian both divorced their then-spouses to marry each other.