Study to Evaluate ALN-CIDEB in Adults With Fibrotic Metabolic Dysfunction-Associated Steatohepatitis (MASH)

Key Inclusion Criteria:

1. A diagnosis of MASH documented in the participant's medical history, or a clinical suspicion of MASH based on non-invasive biomarkers and clinical risk factors, including having a history of 1 or more elements of metabolic syndrome as described in the protocol
2. Screening percutaneous liver biopsy demonstrating a NAFLD Activity Score (NAS) ≥4 and fibrosis stage F2 or F3 as described in the protocol
3. Has a FibroScan Aspartate aminotransferase (FAST) score \>0.35 either at Screening Visit 1 or within approximately 3 months of Screening Visit 1 as described in the protocol

Key Exclusion Criteria:

1. Known chronic liver disease other than Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD), as determined by the investigator as described in the protocol
2. Prior or current suspected or known drug-induced liver injury within approximately 1 year prior to Screening Visit 1
3. History of liver transplantation, current placement on a liver transplant list, or MELD score \>12
4. Known history of alcohol or other substance abuse within the last year or at any time during screening based on investigator's discretion
5. Prior, current, or planned future use of a Glucagon-Like Peptide-1 (GLP-1) receptor agonist-based therapy or any medication approved for the treatment of MASH unless used at a generally stable dose and regimen since at least 3 months prior to Screening Visit 1 or the qualifying historical liver biopsy and use is continued throughout the screening period with no change to the dose or regimen anticipated during the treatment period as described in the protocol

NOTE: Other Protocol-defined Inclusion/Exclusion Criteria Apply