CVE-2026-38991
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedCockpit 2.13.5 and earlier is affected by a misconfiguration within the Bucket component _isFileTypeAllowed function where a specially crafted filename bypasses an extension filter. This allows an authenticated attacker to rename arbitrary files with the .php file extension enabling arbitrary code to be executed on the underlying server.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceCockpit versions 2.13.5 and earlier contain a misconfiguration in the Bucket component's _isFileTypeAllowed function where a specially crafted filename bypasses the extension filter. This allows authenticated attackers to rename arbitrary files to have .php extensions, leading to arbitrary code execution on the server.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Cockpit installation and versionCheck the Cockpit version file (usually VERSION or composer.json in the installation root) or query the /api/version endpoint if accessibleAffected if Installed version is 2.13.5 or earlier
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Confirm Bucket component is presentLocate the Bucket component files in the installation, typically under lib/Cockpit/ or similar path, and verify _isFileTypeAllowed function exists in the Bucket moduleAffected if Bucket component with _isFileTypeAllowed function exists in the installation
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Check file rename permissions for authenticated usersReview user role permissions configuration (usually in config/roles.php or similar) to determine if authenticated users have file rename capabilitiesAffected if Authenticated users or low-privilege roles have permission to rename files in the Bucket component
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Inspect _isFileTypeAllowed function implementationExamine the Bucket component source code for the _isFileTypeAllowed function to verify if extension validation uses a strict whitelist or is vulnerable to bypassAffected if The function does not use strict whitelist-based extension validation or uses a blacklist approach that can be bypassed
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Audit upload directories for suspicious .php filesSearch web-accessible directories (especially assets/, uploads/, or similar folders) for .php files that were likely renamed from other extensionsAffected if Unexpected .php files exist in upload directories, especially files with double extensions or that were recently modified
You are affected if Cockpit version is 2.13.5 or earlier AND the Bucket component with vulnerable _isFileTypeAllowed function is accessible to authenticated users who have file rename permissions.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpdate Cockpit to a version beyond 2.13.5 which contains the proper fix, or implement strict whitelist-based extension validation in the _isFileTypeAllowed function and restrict file rename permissions for authenticated users.
- Consultation3.0 h
- Implementation6.0 h
- Testing5.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,464.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-38991 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-38991 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data