1. Introduction
The Aspen HTTP Server Detection vulnerability allows obtaining the version number of a remote Aspen HTTP server. This information can aid attackers in identifying systems running vulnerable software, potentially leading to targeted attacks. Systems affected are typically those hosting Python web applications using the Aspen framework. A successful exposure of this information has a low impact on confidentiality but could lead to integrity and availability issues if exploited further.
2. Technical Explanation
The vulnerability occurs because the remote host is running an Aspen HTTP server, which is a filesystem dispatch library for Python web frameworks. The version number can be read from the banner exposed by the server. An attacker could identify the specific version of Aspen being used and search for known vulnerabilities associated with that version.
- Root cause: The Aspen HTTP server exposes its version in a publicly accessible banner.
- Exploit mechanism: An attacker connects to the server and reads the exposed banner information to determine the software version. For example, using `curl` or `wget`.
- Scope: Systems running Aspen HTTP Server are affected.
3. Detection and Assessment
To confirm a system is vulnerable, first check if an Aspen HTTP server is running. Then verify that the version number can be obtained from its banner.
- Quick checks: Use `curl -I
` or `wget –server-response ` to inspect the HTTP headers for clues about the server software. - Scanning: Nessus plugin ID 168239 can detect Aspen HTTP Server versions. This is an example only, and results should be verified manually.
- Logs and evidence: Examine web server logs for requests accessing the root directory or common application endpoints.
curl -I http://example.com4. Solution / Remediation Steps
The primary solution is to update Aspen HTTP Server to the latest version, which may include security fixes and banner changes. If an upgrade isn’t immediately possible, consider mitigating exposure through network controls.
4.1 Preparation
- Ensure you have access to the Aspen package manager or deployment tools. A rollback plan involves restoring from the snapshot.
- A change window may be required depending on service criticality and impact.
4.2 Implementation
- Step 1: Update the Aspen HTTP Server package using your system’s package manager (e.g., `pip install –upgrade aspen`).
- Step 2: Restart the web server to apply the changes.
4.3 Config or Code Example
Before
# No specific configuration example available, as banner exposure is inherent in default Aspen behavior.After
# After upgrading Aspen, verify that the server no longer exposes its version number in the HTTP headers.4.4 Security Practices Relevant to This Vulnerability
Regular patching and vulnerability scanning are crucial for identifying and addressing software vulnerabilities like this one. Least privilege can limit the impact of exploitation if an attacker gains access.
- Practice 1: Patch cadence – Regularly update all software components, including web frameworks, to address known security issues.
- Practice 2: Vulnerability scanning – Implement automated vulnerability scans to detect exposed services and outdated versions.
4.5 Automation (Optional)
# Example Ansible task to upgrade Aspen:
# - name: Upgrade Aspen HTTP Server
# pip:
# name: aspen
# state: latest5. Verification / Validation
Confirm the fix by verifying that the server no longer exposes its version number in the HTTP headers. Re-run the initial detection method to confirm the issue is resolved. Perform a basic service smoke test.
- Post-fix check: Run `curl -I http://example.com` and verify that the “Server” header does not contain Aspen or its version number.
- Re-test: Repeat the initial curl command to confirm the banner is no longer exposing the version information.
curl -I http://example.com6. Preventive Measures and Monitoring
Implement security baselines that require regular software updates and vulnerability scanning. Incorporate checks into CI/CD pipelines to prevent deployment of vulnerable versions.
- Baselines: Update your security baseline to include a requirement for regularly patching web frameworks like Aspen.
- Asset and patch process: Establish a regular schedule for reviewing and applying security patches to all systems.
7. Risks, Side Effects, and Roll Back
Upgrading Aspen could introduce compatibility issues with existing applications. Always test changes in a non-production environment first. If problems occur, restore from the pre-upgrade snapshot.
- Roll back: Restore the system from the pre-upgrade snapshot.
8. References and Resources
- Vendor advisory or bulletin: http://aspen.io/en/latest/