CVE-2026-45785 is a medium-severity security vulnerability in OpenMcdf (nuget), affecting versions <= 3.1.3. It is fixed in 3.1.4.
Summary 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. Details The recent Brent's-algorithm commit (24f445a) protects DirectoryTreeEnumerator and works correctly for both attached repros - pure EnumerateEntries() throws FileFormatException: Directory tree contains a loop cleanly. The unprotected code path is the lookup-by-name loop, which is reached from multiple public APIs: RootStorage.OpenStorage(name) / TryOpenStorage(name) RootStorage.OpenStream(name) / TryOpenStream(name) The second one matters most: typical consumers iterate EnumerateEntries() and call OpenStream(entry.Name) per Stream entry. With Brent's algorithm catching the enumeration cycle but not the per-entry lookup, callers can still hang as soon as they touch a streamed entry. PoC Two minimal repros attached, demonstrating the same lookup-loop bug reached via two different public APIs: reprolookup.cfb (5,632 bytes) - hangs on direct OpenStorage(name) for a name not present in the directory reproenumerate.cfb (7,936 bytes) - hangs on OpenStream(entry.Name) called for an entry returned by EnumerateEntries() (the common consumer pattern) Repro 1 - OpenStorage(name) Repro 2 - OpenStream from inside an enumeration loop Both processes will not terminate. (Note: pure foreach (var entry in root.EnumerateEntries()) { } with no per-entry lookup is safe - Brent's algorithm in DirectoryTreeEnumerator catches the enumeration cycle and throws FileFormatException: Directory tree contains a loop. The hang only manifests once a name lookup is performed.) repros.zip Impact 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.
nuget
OpenMcdf (<= 3.1.3)OpenMcdf → 3.1.4 (nuget)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Upgrade OpenMcdf to 3.1.4 or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-45785 is a medium-severity security vulnerability in OpenMcdf (nuget), affecting versions <= 3.1.3. It is fixed in 3.1.4.
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.
OpenMcdf (nuget) versions <= 3.1.3 is affected.
Yes. CVE-2026-45785 is fixed in 3.1.4. Upgrade to this version or later.
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
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.
Upgrade OpenMcdf to 3.1.4 or later.