CVE-2025-53633 Overview
CVE-2025-53633 is a Denial of Service (DoS) vulnerability affecting Chall-Manager, a platform-agnostic system designed to start Challenges on Demand for players. The vulnerability exists in the scenario decoding functionality, where the size of decoded content from zip archives is not validated, potentially allowing attackers to exploit zip bomb decompression attacks that can exhaust system resources.
Critical Impact
Unauthenticated attackers can potentially cause denial of service through zip bomb attacks targeting the scenario decompression functionality, leading to resource exhaustion on affected systems.
Affected Products
- ctfer-io Chall-Manager versions prior to v0.1.4
Discovery Timeline
- July 10, 2025 - CVE-2025-53633 published to NVD
- August 14, 2025 - Last updated in NVD database
Technical Details for CVE-2025-53633
Vulnerability Analysis
This vulnerability is classified under CWE-405 (Asymmetric Resource Consumption/Amplification), which describes security issues where an attacker can cause disproportionate resource consumption relative to the input provided. In the context of Chall-Manager, the scenario processing component accepts zip archives without validating the decompressed size of the contents.
When a malicious zip archive (commonly known as a "zip bomb") is submitted, the application attempts to decompress it without enforcing size limits. Zip bombs exploit the compression ratio of the zip format to create small archives that expand into extremely large files when decompressed, potentially consuming all available disk space or memory on the target system.
The vulnerability does not require authentication or authorization to exploit, making it accessible to any attacker who can reach the Chall-Manager service over the network. However, the vendor notes that Chall-Manager should be deployed deep within infrastructure due to its extensive capabilities, which may limit practical exploitation in properly configured environments.
Root Cause
The root cause of CVE-2025-53633 lies in the absence of size validation during the zip archive decompression process. The original implementation in the scenario decompression code did not track or limit the cumulative size of extracted files, allowing unbounded expansion of compressed content. This missing boundary check enables asymmetric resource consumption where a small malicious input can trigger massive resource utilization.
Attack Vector
The attack vector is network-based, requiring an attacker to submit a specially crafted zip archive to the Chall-Manager scenario processing endpoint. The attack flow involves:
- Attacker crafts a zip bomb archive designed to expand to a size far exceeding its compressed form
- The malicious archive is submitted to the Chall-Manager scenario endpoint
- The vulnerable decompression logic processes the archive without size checks
- System resources (disk space, memory, or CPU) become exhausted during decompression
- Service availability is degraded or completely disrupted
The following code from the security patch in pkg/scenario/decompressor.go demonstrates the fix implementing a new Decompressor structure with size tracking:
+package scenario
+
+import (
+ "archive/zip"
+ "fmt"
+ "io"
+ "os"
+ "path/filepath"
+ "strings"
+
+ errs "github.com/ctfer-io/chall-manager/pkg/errors"
+ "github.com/pkg/errors"
+)
+
+const (
+ blockSize = 1 << 13 // arbitrary
+)
+
+// Decompressor handle the load of
+type Decompressor struct {
+ *Options
+}
+
+type Options struct {
+ MaxSize int64
+
+ currSize int64
+}
+
+// NewDecompressor constructs a fresh Decompressor.
Source: GitHub Commit 14042aa
Detection Methods for CVE-2025-53633
Indicators of Compromise
- Unexpected disk space exhaustion on systems running Chall-Manager
- High memory utilization during scenario processing operations
- Abnormally large temporary files created during zip decompression
- Service crashes or unresponsiveness following scenario upload attempts
Detection Strategies
- Monitor for unusually large or suspiciously small zip files submitted to the scenario endpoint
- Implement file upload logging to track archive submissions and their decompression behavior
- Configure alerts for abnormal resource consumption patterns on Chall-Manager hosts
- Review access logs for repeated scenario upload attempts from single sources
Monitoring Recommendations
- Set up disk space monitoring with alerts when available space drops below critical thresholds
- Implement process monitoring for the Chall-Manager service to detect resource exhaustion
- Configure network traffic analysis to identify potential malicious archive uploads
- Enable logging of file operations during scenario decompression for forensic analysis
How to Mitigate CVE-2025-53633
Immediate Actions Required
- Upgrade Chall-Manager to version v0.1.4 or later immediately
- Ensure Chall-Manager is deployed behind network segmentation as recommended by the vendor
- Implement network access controls to restrict who can reach the Chall-Manager service
- Review existing deployments for signs of exploitation attempts
Patch Information
The vulnerability has been addressed in commit 14042aa and shipped in Chall-Manager version v0.1.4. The fix introduces a new Decompressor structure with configurable MaxSize limits and cumulative size tracking during extraction, preventing zip bomb attacks from exhausting system resources.
Detailed patch information is available:
Workarounds
- Restrict network access to Chall-Manager to trusted internal systems only
- Implement a reverse proxy with file upload size limits in front of Chall-Manager
- Deploy Chall-Manager in isolated containers with resource limits (CPU, memory, disk quotas)
- Monitor and alert on resource consumption to enable rapid response to potential attacks
# Example: Set container resource limits when deploying Chall-Manager
docker run -d \
--name chall-manager \
--memory="2g" \
--memory-swap="2g" \
--cpus="1.0" \
--storage-opt size=10G \
ctfer-io/chall-manager:v0.1.4
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
