CVE-2026-27823
CVE-2026-27823 is a CWE-285 vulnerability in egroupware/egroupware. O3 Security confirms whether CVE-2026-27823 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
EGroupware has a Remote Code Execution Vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27823.
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.
Real-World Exposure
egroupware/egroupware🐘egroupware/egroupwareReal-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 has been identified in EGroupware that may lead to Remote Code Execution (RCE). The issue allows an authenticated attacker to execute arbitrary commands on the server. If user self-registration is enabled, the vulnerability may be exploitable without prior authentication.
The vulnerability stems from improper authorization checks combined with a file write primitive and an arbitrary file read vulnerability, which together enable full system compromise.
Details
1. Improper Authorization in SmallPartMediaRecorder::ajax_upload()
The vulnerability originates in:
EGroupware\SmallParT\Widgets\SmallPartMediaRecorder::ajax_upload()
The function attempts to verify whether the current user is a teacher of the specified course ID before allowing a file upload.
The critical authorization check ensures that the course access control list (ACL) contains:
$required_acl (self::ROLE_TEACHER, i.e., 3)
However, the course_acl value is derived from user-controlled request data.
Bypass Technique
A crafted request can manipulate the participant_role value inside the request body:
{
"video": {
"course_id": {
"participants": [
{
"account_id": "7",
"name": "Test",
"joined_at": "2026-01-10",
"participant_role": 3
}
],
"account_id": "7",
"course_id": "1"
},
"video_hash": ".",
"video_type": "file_here"
}
}
Because the course ACL is taken from participant_role, setting it to 3 allows bypassing the isTeacher check.
2. Arbitrary File Write
After bypassing authorization, the function uploads the provided file into a controllable file path.
The file path is derived from the video_type (or video_path) value, enabling path traversal.
Due to file permission restrictions (server running as www-data), writable targets are limited. One viable target is ./header.inc.php
3. Constraints
Writing a simple PHP webshell may not immediately execute due to OPcache.
An invalid header.inc.php file will break the system and prevent the server from running.
Therefore, a valid file structure must be preserved.
4. Arbitrary File Read
A second vulnerability allows arbitrary file read via:
/egroupware/index.php?menuaction=importexport.importexport_export_ui.download&_filename=../../../usr/share/egroupware/header.inc.php&_suffix=txt&_type=text/plain&filename=leak
The issue resides in:
importexport_export_ui::download
The _filename parameter is user-controlled and used to read arbitrary files.
This allows retrieving the original header.inc.php content.
5. Achieving Remote Code Execution
By combining: Arbitrary file read (to retrieve valid header.inc.php); Arbitrary file write (to overwrite it with modified content), an attacker can inject controlled PHP code while preserving file validity.
This results in Remote Code Execution after server restart, or OPcache expiration. An alternative impact includes modifying the admin setup password to gain full system control.
Impact
Remote Code Execution Full system compromise Arbitrary file read Arbitrary file write Potential complete takeover of EGroupware instance
Reported by
This finding was discovered by Huong Kieu of Cenobe Security (https://cenobe.com/)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | egroupware/egroupware | ≥ 26.0.20251208&&< 26.2.20260224 | 26.2.20260224 |
| 🐘Packagist | egroupware/egroupware | all versions | 23.1.20260224 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for egroupware/egroupware. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update egroupware/egroupware to 26.2.20260224 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27823 is resolved across your whole dependency graph.
Workarounds
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 pinpoints whether CVE-2026-27823 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-27823. 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-2026-27823 in your dependencies?
O3 detects CVE-2026-27823 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.