CVE-2026-45785 in OpenMcdf
Summary
by MITRE • 07/17/2026
OpenMcdf is a fully .NET / C# library to manipulate Compound File Binary File Format files, also known as Structured Storage. In 3.1.3 and earlier, the BST name-lookup loop in DirectoryTree.TryGetDirectoryEntry (OpenMcdf/DirectoryTree.cs:35-46) walks directory entries by repeatedly calling directories.TryGetSibling(child, siblingType, validateColor). A crafted CFB file with cyclic Left/Right sibling links among directory entries, constructed so the per-step BST-order check in TryGetSibling (DirectoryEntries.cs:84-85) is satisfied at every step, drives this while (child is not null) loop forever. There is no cycle detection in TryGetDirectoryEntry, and the bug is reachable from RootStorage.OpenStorage(name), TryOpenStorage(name), OpenStream(name), and TryOpenStream(name), causing an unrecoverable denial of service. This issue is fixed in version 3.1.4.
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Analysis
by VulDB Data Team • 07/17/2026
The vulnerability exists within the OpenMcdf library version 3.1.3 and earlier, which is a .NET/C# implementation for manipulating Compound File Binary Format files commonly known as Structured Storage. This library serves as a critical component for handling legacy file formats in various applications, making its security implications significant. The core issue manifests in the DirectoryTree.TryGetDirectoryEntry method located at OpenMcdf/DirectoryTree.cs lines 35-46 where a binary search tree name-lookup loop operates incorrectly.
The technical flaw occurs when processing crafted CFB files containing cyclic Left/Right sibling links between directory entries. This malicious structure causes the while (child is not null) loop to execute indefinitely because each iteration successfully passes the BST-order validation check implemented in TryGetSibling method at DirectoryEntries.cs lines 84-85. The absence of any cycle detection mechanism within TryGetDirectoryEntry creates a deterministic denial-of-service scenario where the application becomes unresponsive and cannot recover from the infinite loop condition.
The operational impact of this vulnerability extends across multiple entry points within the library's API surface, specifically affecting RootStorage.OpenStorage(name), TryOpenStorage(name), OpenStream(name), and TryOpenStream(name) methods. Any application utilizing these functions to process potentially malicious CFB files will experience complete service unavailability until manually terminated or restarted. This represents a critical security flaw classified under CWE-835 (Loop with Unreachable Exit Condition) which directly maps to the infinite loop behavior described in this vulnerability.
The attack vector requires minimal sophistication as it only necessitates crafting a specific CFB file with cyclic sibling references, making it particularly dangerous for applications that process untrusted file inputs without proper validation. This vulnerability aligns with ATT&CK technique T1499.004 (Endpoint Denial of Service) and demonstrates how seemingly benign file format processing can become a critical attack surface. The fix implemented in version 3.1.4 addresses this by introducing proper cycle detection mechanisms within the directory traversal logic, preventing infinite loops while maintaining the library's core functionality for legitimate file operations.
This vulnerability exemplifies the importance of robust input validation and defensive programming practices when implementing tree traversal algorithms, particularly in security-sensitive applications that handle external data processing. The remediation approach should be considered a best practice for similar scenarios involving hierarchical data structures where cyclic references might occur in malicious inputs. Organizations using OpenMcdf should prioritize upgrading to version 3.1.4 or later to mitigate this persistent denial-of-service risk that could compromise system availability and service continuity.