CVE-2026-45785

OpenMcdf: Uncatchable infinite loop in DirectoryTree.TryGetDirectoryEntry on crafted CFB directory cycle

using OpenMcdf;

using var fs = File.OpenRead("repro_lookup.cfb");
using var root = RootStorage.Open(fs);
root.TryOpenStorage("__substg1.0_3001001F", out _);
// process spins at 100% CPU; Ctrl+C required.

using OpenMcdf;

using var fs = File.OpenRead("repro_enumerate.cfb");
using var root = RootStorage.Open(fs);
foreach (var entry in root.EnumerateEntries())   // safe: Brent's catches enumeration cycles
{
    if (entry.Type == EntryType.Stream)
        _ = root.OpenStream(entry.Name);          // hangs: lookup path has no cycle detection
}

A denial of service affecting any application that opens untrusted CFB files with OpenMcdf. A small crafted input with a cyclic directory tree reaches the unprotected BST name-lookup in DirectoryTree.TryGetDirectoryEntry, hit by any caller of OpenStorage / TryOpenStorage / OpenStream / TryOpenStream - including the very common pattern of iterating EnumerateEntries() and calling OpenStream(entry.Name) per Stream entry. The cycles bypass the per-step BST-order check in TryGetSibling, so no exception is thrown and try/catch cannot protect callers. The affected thread is unrecoverable without killing the process. Downstream CFB consumers (e.g. .msg-file parsers) inherit transitively.

CVE-2026-45785 has a CVSS score of 6.2 (Medium). The vector is requires local access, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.1.4); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

1. What is CVE-2026-45785? CVE-2026-45785 is a medium-severity security vulnerability in OpenMcdf (nuget), affecting versions <= 3.1.3. It is fixed in 3.1.4.
2. How severe is CVE-2026-45785? CVE-2026-45785 has a CVSS score of 6.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of OpenMcdf are affected by CVE-2026-45785? OpenMcdf (nuget) versions <= 3.1.3 is affected.
4. Is there a fix for CVE-2026-45785? Yes. CVE-2026-45785 is fixed in 3.1.4. Upgrade to this version or later.
5. Is CVE-2026-45785 exploitable, and should I be worried? Whether CVE-2026-45785 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-45785 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-45785? Upgrade OpenMcdf to 3.1.4 or later.

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