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How the mentioned CVE works: This vulnerability affects miniserve version 0.32.0 during upload finalization when uploads are enabled. It involves a Time-of-Check Time-of-Use (TOCTOU) race condition combined with symbolic link attacks. The server checks the intended upload path within the document root but then uses it non-atomically for writing. An attacker with access to create or replace filesystem entries in the upload destination can exploit this by inserting a symbolic link after the path validation but before file write operations. By rapidly swapping a regular file with a symlink pointing to arbitrary locations outside the document root, uploaded content can be written to unintended files. This is feasible in shared writable directories or volumes, where the attacker controls file entries. The race window is narrow but exploitable through repeated attempts, potentially leading to overwriting of critical system files or configuration data. The vulnerability stems from insufficient synchronization and secure file handling in the upload process, allowing bypass of path restrictions.
Platform: miniserve
Version: 0.32.0
Vulnerability: TOCTOU symlink race
Severity: Moderate
date: Jan 23 2026
Prediction: Patch expected Jan 30 2026
What Undercode Say:
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!/bin/bash
Check miniserve version
miniserve –version
List upload directory contents
ls -la /upload/path/
Monitor file changes
inotifywait -m /upload/path/
Simulate symlink switching
ln -sf /target/file /upload/path/exploit
while true; do
mv /upload/path/exploit /upload/path/temp;
ln -sf /etc/passwd /upload/path/exploit;
sleep 0.1;
done
How Exploit
1. Identify writable upload directory.
2. Upload initial file to establish path.
3. Create symlink to target file outside root.
- Race condition by swapping symlink during upload finalization.
5. Repeated attempts to overwrite arbitrary files.
Protection from this CVE
Update to patched version.
Use isolated upload directories.
Implement atomic file operations.
Restrict filesystem permissions.
Disable uploads if unnecessary.
Impact
Arbitrary file overwrite.
Data corruption.
Potential privilege escalation.
Service disruption.
Unauthorized access.
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Sources:
Reported By: github.com
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