CVE-2026-120689: Uncontrolled Recursion in HDF5 H5B__iterate_helper() via Crafted File

HDF5 through 2.2.0 contains an uncontrolled recursion vulnerability in H5Biteratehelper() in src/H5B.c. When iterating a version 1 B-tree, the function does not verify that a child node’s level matches the expected level. That check is performed only in H5Bcachedeserialize() when a node is first loaded into the metadata cache. A crafted HDF5 file whose B-tree child pointer refers back to a node already in the cache, such as a node that points to itself, bypasses the check and causes unbounded recursion, leading to stack exhaustion and a crash. This can be triggered by calling H5Ggetinfo() or H5Ggetnumobjs() on a group in the crafted file, which reaches H5Biterate() through H5Gobjinfo() and H5Gstabcount(). An attacker who can get a user or application to open a malicious file can cause a denial of service.