HDF5 Heap Use-After-Free Vulnerability in h5dump (CVE-2026-34734)

CVE-2026-34734 is a heap-use-after-free vulnerability affecting HDF5 versions 1.14.1-2 and earlier. This vulnerability resides within the h5dump helper utility, a component used for displaying the contents of HDF5 files. An attacker can exploit this flaw by crafting a malicious HDF5 file (.h5) that, when processed by a vulnerable version of h5dump, triggers the use-after-free condition. Specifically, the freed object is referenced in a memmove call originating from H5T__conv_struct. The object’s memory is initially allocated by H5D__typeinfo_init_phase3 and subsequently deallocated by H5D__typeinfo_term. Successful exploitation could lead to arbitrary code execution.

Attack Chain

1. The attacker crafts a malicious HDF5 file (.h5) specifically designed to trigger the use-after-free condition.
2. The victim, unknowingly, attempts to examine the contents of the malicious HDF5 file using the vulnerable h5dump utility (version 1.14.1-2 or earlier).
3. h5dump begins parsing the malicious HDF5 file. During this parsing, the H5D__typeinfo_init_phase3 function is called, allocating memory for a data structure.
4. The H5D__typeinfo_term function is subsequently called, prematurely freeing the memory allocated by H5D__typeinfo_init_phase3.
5. Later in the execution, the code attempts to access the previously freed memory within the H5T__conv_struct function, specifically during a memmove operation.
6. This access to freed memory triggers the heap-use-after-free vulnerability.
7. The attacker can potentially control the contents of the freed memory, allowing them to overwrite critical data structures or function pointers.
8. By carefully crafting the HDF5 file, the attacker can leverage the use-after-free to achieve arbitrary code execution on the system.

Impact

Successful exploitation of CVE-2026-34734 can lead to arbitrary code execution in the context of the user running the h5dump utility. This could allow an attacker to gain complete control over the affected system, potentially leading to data theft, system compromise, or denial of service. The vulnerability affects anyone using the HDF5 library to process potentially untrusted HDF5 files.

Recommendation

• Upgrade HDF5 to a version later than 1.14.1-2 to patch CVE-2026-34734 (reference: CVE-2026-34734).
• Monitor process execution for instances of h5dump being invoked with untrusted or potentially malicious HDF5 files to identify potential exploitation attempts (reference: Sigma rule “Detect h5dump Execution with Suspicious File Arguments”).
• Implement input validation on HDF5 files before processing them with h5dump to prevent malicious files from triggering the vulnerability (reference: Sigma rule “Detect h5dump Accessing Files From Suspicious Locations”).