Summary
OpenMcdf has an Infinite loop DoS via crafted CFB directory cycle
OpenMcdf does not detect cycles in the directory entry red-black tree of a Compound File Binary (CFB) document. A crafted CFB file with a cycle in the LeftSiblingID / RightSiblingID chain causes Storage.EnumerateEntries() and Storage.OpenStream() to loop indefinitely, consuming the calling thread with no possibility of recovery via try/catch.
Details
CFB directory entries form a red-black tree linked by LeftSiblingID and RightSiblingID fields. OpenMcdf's DirectoryTreeEnumerator and DirectoryTree.TryGetDirectoryEntry traverse this tree without tracking visited node IDs, so a crafted cycle (e.g. entry A's RightSiblingID points to entry B, and entry B's LeftSiblingID points back to entry A) causes traversal to loop indefinitely.
Two distinct code paths are affected:
Storage.EnumerateEntries()-DirectoryTreeEnumerator.MoveNext()never returnsfalse; the same entry is yielded on every iteration and the caller'sforeachnever exits. Heap grows unboundedly as entries accumulate.Storage.OpenStream()-DirectoryTree.TryGetDirectoryEntryloops indefinitely insideDirectoryEntries.TryGetSiblingduring the name lookup.
PoC
A crafted CFB file with a sibling cycle (see attached) triggers the issue with the following code:
using OpenMcdf;
using var ms = new MemoryStream(File.ReadAllBytes("crafted.cfb"));
using var root = RootStorage.Open(ms);
// Never returns - EnumerateEntries loops indefinitely
foreach (var entry in root.EnumerateEntries())
{
Console.WriteLine(entry.Name);
if (entry.Type == EntryType.Stream)
root.OpenStream(entry.Name); // also hangs depending on the cycle structure
}
Impact
A denial of service affecting any application that opens untrusted CFB files with OpenMcdf. A small crafted input carrying a valid CFB magic header (D0 CF 11 E0 A1 B1 1A E1) is sufficient to pass initial format validation and reach the vulnerable traversal code. No exception is thrown, so try/catch cannot protect callers. The affected thread is unrecoverable without killing the process.
CVE-2026-41511 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 (3.1.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
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.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-41511? CVE-2026-41511 is a medium-severity security vulnerability in OpenMcdf (nuget), affecting versions < 3.1.3. It is fixed in 3.1.3.
- How severe is CVE-2026-41511? CVE-2026-41511 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.
- Which versions of OpenMcdf are affected by CVE-2026-41511? OpenMcdf (nuget) versions < 3.1.3 is affected.
- Is there a fix for CVE-2026-41511? Yes. CVE-2026-41511 is fixed in 3.1.3. Upgrade to this version or later.
- Is CVE-2026-41511 exploitable, and should I be worried? Whether CVE-2026-41511 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
- What actually determines whether CVE-2026-41511 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.
- How do I fix CVE-2026-41511? Upgrade
OpenMcdfto 3.1.3 or later.