CVE-2023-33251 Overview
CVE-2023-33251 is an insecure permissions vulnerability affecting Lightbend Akka HTTP before version 10.5.2. When the framework accepts file uploads via the FileUploadDirectives.fileUploadAll directive, temporary files are created with overly permissive access rights. This allows other local users on Linux or UNIX systems to read the contents of uploaded files, potentially exposing sensitive data. This vulnerability is similar to CVE-2022-41946, which affected another component with comparable insecure temporary file handling.
Critical Impact
Sensitive file uploads processed by Akka HTTP applications may be readable by unauthorized local users, leading to information disclosure of potentially confidential data.
Affected Products
- Lightbend Akka HTTP versions prior to 10.5.2
- Linux Kernel (as the underlying operating system)
- Applications using the FileUploadDirectives.fileUploadAll directive
Discovery Timeline
- 2023-05-21 - CVE-2023-33251 published to NVD
- 2025-01-31 - Last updated in NVD database
Technical Details for CVE-2023-33251
Vulnerability Analysis
This vulnerability falls under CWE-732 (Incorrect Permission Assignment for Critical Resource). When Akka HTTP processes file uploads using the fileUploadAll directive, the framework creates temporary files to store the uploaded content during processing. The core issue is that these temporary files are created with world-readable permissions (typically 0644 or similar), rather than restrictive permissions that would limit access to only the application owner.
On multi-user Linux and UNIX systems, this means any authenticated local user can potentially read the contents of files being uploaded to the application. The local attack vector requires an attacker to have existing access to the system, but once present, they can monitor temporary directories for newly created files and exfiltrate their contents before the application completes processing and removes them.
Root Cause
The root cause lies in the default file permission mask used when creating temporary files during the file upload handling process. The Akka HTTP framework did not explicitly set restrictive permissions when invoking file creation operations, allowing the system's default umask to determine the final permissions. In many system configurations, this results in files that are readable by all users on the system.
Attack Vector
The attack requires local access to the system running the vulnerable Akka HTTP application. An attacker with a local user account can monitor the temporary file directory (typically /tmp or a configured upload directory) for new files created during upload operations. Using file system monitoring tools or simple polling scripts, the attacker can detect and read these temporary files before they are processed and deleted.
The vulnerability is particularly concerning in shared hosting environments, containerized deployments with shared storage, or any multi-tenant system where multiple users have local access. The attacker does not need elevated privileges—any local user account is sufficient to exploit this vulnerability.
Detection Methods for CVE-2023-33251
Indicators of Compromise
- Unusual read access patterns to temporary directories by non-application users
- Monitoring or enumeration scripts targeting /tmp or application upload directories
- Unexpected file access logs showing reads of temporary upload files by unauthorized accounts
- Presence of file monitoring tools like inotifywait running under suspicious user accounts
Detection Strategies
- Monitor file access logs for temporary directories where Akka HTTP stores uploads
- Implement file integrity monitoring on temporary upload directories
- Audit local user access to systems running Akka HTTP applications
- Review application logs for unusual upload patterns that might indicate reconnaissance
Monitoring Recommendations
- Enable auditd rules to track read operations on temporary file directories
- Configure SentinelOne to alert on suspicious file access patterns in upload directories
- Implement regular permission audits on temporary files created by applications
- Monitor for unauthorized local user activity on application servers
How to Mitigate CVE-2023-33251
Immediate Actions Required
- Upgrade Akka HTTP to version 10.5.2 or later immediately
- Review systems for evidence of exploitation or unauthorized file access
- Audit local user accounts on affected systems and remove unnecessary access
- Consider implementing temporary directory isolation for sensitive applications
Patch Information
Lightbend has addressed this vulnerability in Akka HTTP version 10.5.2. The patch ensures that temporary files created during file upload processing are created with restrictive permissions that prevent access by other users. Organizations should upgrade to the patched version as the primary remediation strategy.
For detailed patch information, refer to the Akka HTTP CVE-2023-05-15 Advisory and the Akka HTTP Security Announcement.
Workarounds
- Configure a dedicated temporary directory with restrictive permissions (e.g., chmod 700) for file uploads
- Set a restrictive umask (e.g., 0077) for the application process before starting
- Run the Akka HTTP application under a dedicated user account with isolated home directory
- Consider implementing additional access controls using SELinux or AppArmor profiles
# Configuration example - Set restrictive umask before starting application
umask 0077
# Create dedicated temp directory with restricted permissions
mkdir -p /var/app/uploads/tmp
chmod 700 /var/app/uploads/tmp
chown appuser:appgroup /var/app/uploads/tmp
# Export temp directory for application
export TMPDIR=/var/app/uploads/tmp
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
