CVE-2026-19027 in HDF5
Summary
by MITRE • 08/06/2026
The H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic functions in H5Znbit.c in HDF5 through 2.3.0 advance a read index into the compressed chunk buffer without bounding it against the buffer's actual size. This allows attackers to cause an out-of-bounds heap read, and in constrained cases disclosure of adjacent heap memory into decompressed dataset values, via a crafted HDF5 file whose N-Bit filter parameters describe more decompressed data than the stored compressed chunk actually contains, triggered via H5Dread, e.g. by the h5ls or h5repack tools.
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Analysis
by VulDB Data Team • 08/06/2026
The vulnerability described represents a critical heap-based buffer over-read condition affecting the HDF5 library's N-Bit compression filter implementation. This issue manifests in three specific functions within the H5Znbit.c source file: H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic. The root cause stems from inadequate bounds checking during decompression operations where the read index advances through compressed data without proper validation against the actual buffer size limits. This fundamental flaw creates a pathway for attackers to manipulate the decompression process by crafting specially designed HDF5 files that contain malformed N-Bit filter parameters. When these malicious files are processed through standard HDF5 operations such as H5Dread, which is invoked by command-line utilities like h5ls and h5repack, the library's decompression routines execute with insufficient input validation, leading to unauthorized memory access patterns.
The technical exploitation of this vulnerability follows a precise sequence where attacker-controlled data structures within the N-Bit filter parameters specify decompressed data sizes that exceed the actual compressed chunk boundaries. During decompression, the functions advance their internal read pointers beyond the legitimate buffer limits, causing heap memory reads that extend beyond allocated boundaries. This out-of-bounds access can potentially expose adjacent heap memory regions to the decompressed output, creating a information disclosure scenario where sensitive data from neighboring memory locations becomes accessible through the corrupted dataset values. The vulnerability specifically affects HDF5 versions up to and including 2.3.0, making it particularly concerning given the widespread use of this library in scientific computing, data storage systems, and various applications requiring robust binary data handling capabilities.
The operational impact of this vulnerability extends beyond simple memory corruption to encompass potential security implications for systems processing untrusted HDF5 data. Attackers could leverage this weakness to extract sensitive information from heap memory, potentially including cryptographic keys, user credentials, or other confidential data stored in adjacent memory regions. The attack vector requires the target system to process a crafted HDF5 file through any of the affected decompression functions, which commonly occurs during routine data access operations with tools like h5ls for listing dataset contents or h5repack for data manipulation and repacking. This makes the vulnerability particularly dangerous in environments where users might encounter untrusted HDF5 files or when automated systems process such data without proper input validation. The vulnerability aligns with CWE-129, which addresses improper validation of buffer boundaries, and represents a clear violation of secure coding practices that should prevent unauthorized memory access patterns.
Mitigation strategies for this vulnerability require immediate patching of affected HDF5 installations to version 2.4.0 or later where the bounds checking has been properly implemented. System administrators should ensure all HDF5-based applications are updated and that users cannot process untrusted data files without proper validation mechanisms in place. Input sanitization should be enforced at multiple levels including application interfaces, library calls, and file format validation routines. Additionally, monitoring systems should be configured to detect unusual memory access patterns or out-of-bounds read operations during HDF5 processing activities. The ATT&CK framework categorizes this vulnerability under T1059 for execution of malicious code through data manipulation and potentially T1566 for initial access via malicious file delivery. Organizations should implement strict file validation policies for any data sources that may contain HDF5 files, particularly those originating from external or untrusted environments where crafted malicious inputs could be introduced.