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CVE-2026-41511 medium CVSS 6.2

Vulnerability in OpenMcdf (CVE-2026-41511)

Summary

Vulnerability in OpenMcdf (CVE-2026-41511). Risk of unauthorized operations or information disclosure. Exploitable via LeftSiblingID. Mitigation: upgrade to 3.1.3 or later.

Original description

The description as published by the source.

Summary

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 returns false; the same entry is yielded on every iteration and the caller's foreach never exits. Heap grows unboundedly as entries accumulate.
  • Storage.OpenStream() - DirectoryTree.TryGetDirectoryEntry loops indefinitely inside DirectoryEntries.TryGetSibling during 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…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-41511 has been found in OpenMcdf.
Attackers can target a specific entry point like LeftSiblingID over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.2/10.
What to do: upgrade OpenMcdf to 3.1.3 or later.
If unsure, ask your IT team or search "OpenMcdf CVE-2026-41511" on the vendor's site.

CVE-2026-41511 (OpenMcdf) — CWE-835 / CVSS v3 6.2
Attack vector: local / unauthenticated / no user interaction
Attack surface: LeftSiblingID / RightSiblingID / DirectoryTreeEnumerator / DirectoryTree.TryGetDirectoryEntry
Patched: 3.1.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-835) exists in OpenMcdf. Attackers reach the vulnerable code path via LeftSiblingID without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of OpenMcdf. Attack surface: LeftSiblingID / RightSiblingID / DirectoryTreeEnumerator / DirectoryTree.TryGetDirectoryEntry.

🔥 Severity

Severity: Medium (CVSS 6.2/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 3.1.3.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'OpenMcdf' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'OpenMcdf' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で OpenMcdf を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade OpenMcdf to 3.1.3

    ステージング環境で 3.1.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

nuget OpenMcdf
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.3"}]}]

References

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