CVE-2026-50776: Pronis Loisirs Billetterie Path Traversal

CVE-2026-50776 Overview

CVE-2026-50776 is a directory traversal vulnerability affecting Pronis Loisirs Billetterie CSE versions released before April 2026. A remote attacker can traverse the file system to access files outside the intended directory. The flaw enables retrieval of sensitive information and, according to the advisory, arbitrary code execution.

The weakness is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The vulnerability is exploitable over the network without authentication or user interaction.

Critical Impact
Unauthenticated remote attackers can read sensitive files from the host and, per the vendor advisory, execute arbitrary code against Pronis Loisirs Billetterie CSE deployments.

Affected Products

Pronis Loisirs Billetterie CSE versions prior to April 2026 (< 04/2026)
Vendor homepage: Pronis Loisirs
Specific CPE identifiers are not published in the NVD entry

Discovery Timeline

2026-08-17 - CVE-2026-50776 published to NVD
2026-08-18 - Last updated in NVD database

Technical Details for CVE-2026-50776

Vulnerability Analysis

The vulnerability exists in the Pronis Loisirs Billetterie CSE ticketing application, a French works-council (Comité Social et Économique) benefits platform. The application fails to properly restrict pathname inputs supplied through HTTP requests. An attacker submits crafted path sequences that escape the intended base directory and reach arbitrary locations on the server file system.

Because exploitation requires no privileges, no user interaction, and only network access, an attacker can weaponize the flaw remotely. The advisory states that successful traversal can also lead to arbitrary code execution, which typically occurs when attacker-controlled files are placed in or read from executable locations, or when the application dereferences traversed paths for inclusion.

The published EPSS probability indicates a modest but measurable likelihood of exploitation activity within 30 days of publication.

Root Cause

The root cause is improper input validation on file path parameters. The application accepts user-controlled input and concatenates it into file system operations without canonicalizing paths or rejecting traversal sequences such as ../, encoded variants (%2e%2e%2f), or absolute paths. This maps directly to [CWE-22].

Attack Vector

The attack vector is network-based. An unauthenticated attacker issues HTTP requests to a vulnerable endpoint that consumes a file name or path parameter. The attacker inserts traversal sequences to reference files outside the web root, such as configuration files, credential stores, or session data.

Where the traversal reaches an inclusion or upload sink, the attacker may pivot to arbitrary code execution by referencing writable or executable paths. Public technical detail is available in the Henkel-CyberVM CVE repository.

Detection Methods for CVE-2026-50776

Indicators of Compromise

HTTP requests containing ../, ..\, or URL-encoded variants (%2e%2e%2f, %252e%252e%252f) against Pronis Loisirs Billetterie endpoints
Web server access to sensitive file paths such as /etc/passwd, web.config, .env, or application configuration files originating from the Billetterie process
Unexpected outbound connections or new files written under application directories following suspicious path parameters
Anomalous HTTP 200 responses to requests referencing non-standard file extensions or absolute paths

Detection Strategies

Deploy web application firewall (WAF) rules that block path traversal sequences and canonicalize decoded paths before evaluation
Correlate application logs with file system audit events to flag reads of files outside the application's expected directory tree
Enable request body and query-string logging on the Billetterie web server and hunt for traversal patterns in URI, referer, and body fields

Monitoring Recommendations

Alert on repeated 4xx responses followed by a successful 2xx to the same endpoint with traversal characters, indicating filter evasion
Monitor for new process spawns from the web application user account, which would indicate escalation from file read to code execution
Baseline outbound traffic from the ticketing server and alert on deviations, such as connections to unfamiliar hosts after suspicious requests

How to Mitigate CVE-2026-50776

Immediate Actions Required

Upgrade Pronis Loisirs Billetterie CSE to the April 2026 release or later as soon as the vendor makes it available
Contact Pronis Loisirs directly through the official homepage to confirm the patched build and coordinate deployment
Restrict network access to the Billetterie web interface, permitting only trusted networks or VPN clients until patching completes
Rotate any credentials, API keys, or session secrets stored on the application host, as they may have been exposed

Patch Information

The advisory identifies vulnerable versions as those released before April 2026. Administrators should install the fixed release from Pronis Loisirs and validate the version string after upgrade. Refer to the GitHub CVE repository entry for the latest published references.

Workarounds

Place a reverse proxy or WAF in front of the application with rules that reject traversal sequences and normalize URIs before forwarding
Enforce least-privilege file system permissions on the application service account so that sensitive files are unreadable even if traversal succeeds
Disable or remove any file-serving endpoints that accept user-controlled path parameters until the patched release is deployed

bash

# Example ModSecurity rule blocking common traversal patterns
SecRule REQUEST_URI|ARGS|REQUEST_HEADERS "@rx (?:\.\./|\.\.\\|%2e%2e%2f|%2e%2e/|\.\.%2f)" \
    "id:1050776,phase:2,deny,status:403,log,\
    msg:'CVE-2026-50776 Pronis Billetterie path traversal attempt'"