CVE-2026-45785 OpenMcdf: Uncatchable infinite loop in DirectoryTree.TryGetDirectoryEntry on crafted CFB directory cycle
Attackers can cause an infinite loop and denial of service in OpenMcdf by providing a crafted Compound File Binary file with cyclic directory entries.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45785?
CVE-2026-45785 is a medium-severity denial of service vulnerability in openmcdf, published on 17 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-835
Which versions are affected by CVE-2026-45785?
2 open source packages ship an affected version, including OpenMcdf.
| Package | Affected | Fixed in |
|---|---|---|
OpenMcdf NuGet | All versions | 3.1.4 |
OpenMcdf NuGet | All versions | 3.1.4 |
How do I fix CVE-2026-45785?
Upgrade OpenMcdf to 3.1.4 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-45785 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45785 exists.
Sources
Also known as GHSA-5qwm-7pvp-w988.