CVE-2026-41309 Overview
Open Source Social Network (OSSN) versions prior to 9.0 contain a resource exhaustion vulnerability (CWE-400) that enables attackers to cause a Denial of Service (DoS) condition through malicious image uploads. An attacker can upload a specially crafted image with extreme pixel dimensions (e.g., 10000 × 10000 pixels). While the compressed file size on disk may be small, the server attempts to allocate significant memory and CPU cycles during the decompression and resizing process, leading to service unavailability.
Critical Impact
Unauthenticated remote attackers can exhaust server resources by uploading crafted images with extreme dimensions, causing Denial of Service conditions affecting all users of the social networking platform.
Affected Products
- Open Source Social Network (OSSN) versions prior to 9.0
- PHP-based deployments processing user-uploaded images
- Systems with inadequate memory and execution time limits configured
Discovery Timeline
- April 24, 2026 - CVE-2026-41309 published to NVD
- April 29, 2026 - Last updated in NVD database
Technical Details for CVE-2026-41309
Vulnerability Analysis
This vulnerability is classified as Uncontrolled Resource Consumption (CWE-400) and affects the image upload functionality in OSSN. The root issue lies in the lack of validation for image pixel dimensions before server-side processing begins. While most systems validate file size, they often overlook the decompressed memory footprint of images. A highly compressed image file (e.g., a few hundred kilobytes) can decompress to consume gigabytes of memory when its pixel dimensions are extreme.
When a user uploads an image, the OSSN application processes it for resizing and thumbnail generation. Without proper dimension checks, the server attempts to load the entire decompressed image into memory, allocating memory proportional to width × height × bytes-per-pixel. For a 10000 × 10000 pixel image with 4 bytes per pixel (RGBA), this translates to approximately 400MB of memory per image. Multiple concurrent uploads can quickly exhaust available server resources.
Root Cause
The vulnerability exists in the OssnFile.php class where image uploads were processed without validating pixel dimensions. Prior to version 9.0, the application did not check image width and height headers before attempting to decompress and resize uploaded images. This allowed attackers to bypass file size restrictions by using highly compressed images with extreme dimensions.
Attack Vector
The attack is network-accessible and requires no authentication or user interaction. An attacker can exploit this vulnerability by:
- Creating a highly compressed image file (PNG or similar format) with extreme pixel dimensions
- Uploading the image through any OSSN image upload endpoint
- The server attempts to decompress and resize the image, consuming excessive memory and CPU
- Repeated uploads can exhaust server resources, causing denial of service for legitimate users
}
//post size error
//post_size < upload max size
- if(!empty($_SERVER['CONTENT_LENGTH']) && empty($_POST)){
+ if(!empty($_SERVER['CONTENT_LENGTH']) && empty($_POST)) {
$this->error = UPLOAD_ERR_FORM_SIZE;
}
if(isset($this->file) && ($this->file['error'] !== UPLOAD_ERR_OK || $this->file['size'] == 0)) {
ossn_trigger_message($this->getFileUploadError($this->file['error']), 'error');
redirect($this->redirect);
}
+ if(isset($this->file) && preg_match('/image/i', $this->file['type'])) {
+ $fileTmpPath = $this->file['tmp_name'];
+
+ // Read image headers safely without loading the full image
+ $imageInfo = @getimagesize($fileTmpPath);
+ if($imageInfo === false) {
+ $this->error = UPLOAD_ERR_NO_FILE;
+ redirect($this->redirect);
+ }
+
+ $width = $imageInfo[0];
+ $height = $imageInfo[1];
+
+ //OSSN Vulnerability report: CWE-400 - Uncontrolled Resource Consumption
+ // Set maximum allowed dimensions
+ $image_max_dim = ossn_call_hook('file', 'max:dimensions', $this->file, array(
+ 'width' => 5000,
+ 'height' => 5000,
Source: GitHub Commit Update
Detection Methods for CVE-2026-41309
Indicators of Compromise
- Unusual spikes in server memory consumption during image upload operations
- PHP processes consuming excessive CPU time with max_execution_time warnings
- Multiple failed or timed-out image upload requests from the same source
- Error logs showing memory allocation failures during image processing
- Increased occurrence of HTTP 500 errors on image upload endpoints
Detection Strategies
- Monitor PHP process memory usage and set alerts for abnormal consumption patterns during uploads
- Implement application-level logging to track image upload dimensions before processing
- Configure web application firewalls (WAF) to analyze image headers and block uploads exceeding dimension thresholds
- Deploy SentinelOne Singularity to detect resource exhaustion patterns and anomalous process behavior
Monitoring Recommendations
- Set up resource utilization dashboards to track memory and CPU consumption on web servers
- Enable PHP-FPM slow log monitoring to identify image processing functions taking excessive time
- Configure alerts for sudden increases in HTTP 503 (Service Unavailable) responses
- Monitor upload directories for images with suspicious dimension-to-file-size ratios
How to Mitigate CVE-2026-41309
Immediate Actions Required
- Upgrade to OSSN version 9.0 or later which introduces stricter validation of image dimensions
- Implement server-side checks on image headers to reject files exceeding 4000 × 4000 pixels before processing
- Adjust php.ini settings to strictly limit memory_limit and max_execution_time values
- Deploy rate limiting on image upload endpoints to prevent rapid exploitation attempts
Patch Information
The vulnerability is addressed in OSSN version 9.0 through the implementation of stricter image dimension validation in the OssnFile.php class. The patch uses getimagesize() to safely read image headers without loading the full image into memory, then compares dimensions against configurable maximum values (default 5000 × 5000 pixels). For detailed information, refer to the GitHub Security Advisory and the patch commit.
Workarounds
- Implement client-side JavaScript validation to reject images exceeding reasonable pixel dimensions before upload
- Add server-side pre-processing checks using getimagesize() to validate dimensions before full image processing
- Configure PHP resource limits to minimize impact: set memory_limit to 128M and max_execution_time to 30
- Use a reverse proxy or WAF to inspect image uploads and block those with extreme dimensions
# Configuration example
# Modify php.ini to limit resource consumption
memory_limit = 128M
max_execution_time = 30
upload_max_filesize = 10M
post_max_size = 12M
# Restart PHP-FPM to apply changes
sudo systemctl restart php-fpm
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
