CVE-2026-27891 is a high-severity (CVSS 7.2) Improper Input Validation vulnerability in facturascripts/facturascripts. No vendor fix is recorded yet; mitigation options are listed below.
Remote Code Execution (RCE) via Zip Slip in Plugin Upload Mechanism
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27891.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-27891 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
facturascripts/facturascriptsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Summary
A Critical vulnerability exists in the Plugins::add() function. The system fails to properly validate the file paths within uploaded ZIP archives. This allows an attacker to perform a Zip Slip attack, leading to Arbitrary File Write and Remote Code Execution (RCE) by overwriting sensitive .php files outside the designated plugins directory.
Details
The vulnerability is located in Plugins.php. While the testZipFile function attempts to validate that the ZIP contains only one root folder, it does not sanitize or validate the individual file paths within that folder.
// Vulnerable logic in Plugins.php
for ($index = 0; $index < $zipFile->numFiles; $index++) {
$data = $zipFile->statIndex($index);
$path = explode('/', $data['name']);
if (count($path) > 1) {
$folders[$path[0]] = $path[0];
}
}
An attacker can bypass this check by naming a file ValidPluginName/../../shell.php. The explode function will see ValidPluginName as the root folder, satisfying the count($folders) != 1 check. However, during extraction, the ../../ sequence triggers a path traversal, allowing the file to be written anywhere the web server has permissions the root directory.
PoC
Prepare Malicious ZIP: Use a tool (like evilarc) or a script to create a ZIP file where one of the entries is named: MyPlugin/../../rce.php
Inject Payload: Inside rce.php, put a simple shell:
<?php system($_GET['cmd']); ?>
Upload: Navigate to the "Add Plugin" section in FacturaScripts and upload the malicious ZIP.
Execution: Access the shell via https://target.com/rce.php?cmd=whoami.
Impact
Confidentiality: High (Attacker can read all database configs and files). Integrity: High (Attacker can modify any file on the server). Availability: High (Attacker can delete the entire installation).
https://github.com/ZeroXJacks/CVEs/blob/main/2026/CVE-2026-27891.md
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | facturascripts/facturascripts | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for facturascripts/facturascripts, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of facturascripts/facturascripts has shipped for CVE-2026-27891 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27891 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-27891. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27891 in your dependencies?
O3 Security finds CVE-2026-27891 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.