CVE-2025-53632: 
vulnerability analysis and mitigation

CVE-2025-53632 is a zip slip (path traversal) vulnerability in ctfer-io/chall-manager, a platform-agnostic system for starting Capture-the-Flag challenges on demand. The flaw exists in the scenario decoding process, where zip archive file paths are not validated before extraction, allowing files to be written outside the intended directory. All versions prior to 0.1.4 of the Go module github.com/ctfer-io/chall-manager are affected. The vulnerability was published on July 10, 2025, with a patch shipped the same day. It carries a CVSS v3.1 base score of 9.1 (Critical) and a CVSS v4.0 base score of 8.8 (High) (Github Advisory, GitHub Security Advisory).

The root cause is CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), specifically a classic "zip slip" pattern. In pkg/scenario/io.go, the Decode function used filepath.Join(cd, f.Name) to construct the output path for each file in a zip archive without verifying that the resulting path remained within the intended extraction directory (cd). An attacker can craft a zip archive containing entries with path traversal sequences (e.g., ../../etc/cron.d/malicious) so that when the archive is decoded, files are written to arbitrary locations on the filesystem. No authentication or authorization is required to trigger this code path. The fix, implemented in commit 47d188f, introduces a sanitizeArchivePath function that checks whether the resolved path has the expected directory prefix before writing (GitHub Commit, Github Advisory).

Successful exploitation allows an unauthenticated attacker to write arbitrary files to any location accessible by the chall-manager process, resulting in high integrity and high availability impact. Attackers can overwrite critical system files (e.g., cron jobs, SSH authorized keys, service configurations) to achieve persistent code execution, or corrupt application files to cause denial of service. Confidentiality is not directly impacted by this vulnerability, but arbitrary file write primitives can facilitate privilege escalation and lateral movement within the infrastructure (Github Advisory, GitHub Security Advisory).

A public proof-of-concept exploit is available at https://github.com/pandatix/CVE-2025-53632, published by the same researcher (pandatix) who disclosed the vulnerability (PoC on GitHub). No authentication or special privileges are required, making the attack surface broad for any network-reachable chall-manager instance. The EPSS score is approximately 0.15–0.195%, placing it in the 41st percentile for exploitation likelihood within 30 days. There is no current evidence of in-the-wild exploitation or CISA KEV catalog listing, and no specific threat actor attribution has been reported (Github Advisory).

1. Reconnaissance: Identify exposed chall-manager instances on the network. Because the project recommends deep infrastructure burial, scan internal networks or CI/CD environments for the service's gRPC or HTTP endpoints.
2. Craft malicious zip archive: Create a zip file containing one or more entries with path traversal sequences in their filenames, such as ../../etc/cron.d/backdoor or ../../root/.ssh/authorized_keys, pointing to a target file outside the intended extraction directory.
3. Submit the malicious scenario: Send the crafted zip archive (base64-encoded as required by the API) to the chall-manager scenario decoding endpoint without any authentication credentials.
4. Trigger extraction: The vulnerable Decode function in pkg/scenario/io.go calls filepath.Join(cd, f.Name) without path validation, causing the file to be written to the attacker-controlled path on the server filesystem.
5. Achieve objective: Depending on the written file's location and content — e.g., a cron job, SSH key, or web shell — the attacker gains persistent access, code execution, or denial of service on the host (Github Advisory, GitHub Commit).

• File System: Unexpected files created outside the chall-manager scenario extraction directory (e.g., new entries in /etc/cron.d/, /root/.ssh/authorized_keys, or web-accessible directories); modification timestamps on system files coinciding with scenario decode operations.
• Logs: Application logs showing scenario decode requests followed by ErrInternal errors (post-patch) or, on unpatched systems, successful writes to unusual paths; OS-level audit logs (auditd) recording file creation events by the chall-manager process in sensitive directories.
• Process: Unexpected processes spawned by the chall-manager service account (e.g., reverse shells, cron-triggered scripts) shortly after a scenario upload event.
• Network: Inbound requests to the chall-manager API endpoint submitting unusually large or structurally anomalous base64-encoded zip payloads; outbound connections from the server to unknown external IPs following scenario decoding.

The vendor has released a patch in chall-manager version v0.1.4, which introduces path sanitization via the sanitizeArchivePath function in pkg/scenario/io.go (commit 47d188f). Organizations should upgrade to v0.1.4 or later immediately. No configuration-based workaround exists according to the official advisory; the only compensating control is to ensure chall-manager is deployed deep within the infrastructure with strict network-level access controls so that untrusted users cannot reach the service endpoint (GitHub Release, Github Advisory).

The vulnerability was discovered and disclosed by researcher pandatix (Lucas Tesson), who also authored the fix and published a proof-of-concept. The advisory was reviewed and published to the GitHub Advisory Database on July 10, 2025. No significant broader media coverage or notable community commentary beyond the GitHub advisory and PoC repository has been identified (Github Advisory, PoC on GitHub).