Versa Concerto 0-Day Flaw Enables Remote Code Execution by Bypassing Authentication

Security researchers have uncovered multiple critical vulnerabilities in Versa Concerto, a widely deployed network security and SD-WAN orchestration platform used by large enterprises, service providers, and government entities.

Despite responsible disclosure efforts over a 90-day period, these vulnerabilities remain unpatched, creating significant risk for organizations using this platform.

The issues include authentication bypass flaws, arbitrary file write vulnerabilities, and container escape techniques that, when chained together, allow attackers to fully compromise both the application and underlying host system.

Researchers identified a fundamental security flaw in Versa Concerto’s authentication mechanism stemming from inconsistent URL processing.

To understand the appliance’s routing, we start by analyzing the Traefik container. The Traefik container listens on ports 80/443, serving as the entry point for client requests. Based on location configurations, incoming requests are routed to either core-service or web-service.

The application’s AuthenticationFilter class contains a Time-of-Check to Time-of-Use (TOCTOU) vulnerability where the REQUEST_URI undergoes URL decoding during authentication checks, but remains unencoded when processed by controllers.

This inconsistency allows attackers to bypass authentication using specially crafted URLs containing encoded path traversal characters.

The exploit leverages paths like /portalapi/v1/users/username/admin;%2fv1%2fping where the semicolon followed by URL-encoded slashes tricks the authentication system.

When the system processes this URL for authentication, it decodes the path and misidentifies it as an excluded endpoint, granting unauthorized access.

This vulnerability exposes sensitive API endpoints that would normally require proper authentication, providing an entry point for further attacks.

Chained Exploitation Leads to Remote Code Execution

After gaining unauthorized access, attackers can exploit a vulnerable file upload endpoint in the web-service component that allows arbitrary file writes through a race condition vulnerability.

The authentication bypass serves as the initial entry point in a sophisticated attack chain.

Although uploaded files are quickly deleted, researchers demonstrated that precisely timed requests could successfully exploit this window of opportunity.

By leveraging this file write capability, attackers can employ an LD_PRELOAD technique to achieve remote code execution.

The exploit involves overwriting /etc/ld.so.preload with a path to a malicious shared object file simultaneously uploaded to /tmp/hook.so.

This malicious object executes when triggered by periodic system commands, establishing reverse shell access to the container.

Further escalation to the host system is possible through a critical Docker misconfiguration.

The container has /usr/bin/ and /bin/ directories mapped directly to the host’s filesystem, allowing attackers to replace system binaries with malicious versions that execute when triggered by scheduled cron jobs like /etc/cron.d/popularity-contest.

CVE Assignments and Temporary Mitigation Measures

After multiple unsuccessful attempts to receive patches from Versa, VulnCheck assigned three CVEs to the vulnerabilities: CVE-2025-34025 for the Docker container escape, CVE-2025-34026 for the actuator authentication bypass, and CVE-2025-34027 for the authentication bypass leading to remote code execution.

According to the Report, Organizations using Versa Concerto should implement immediate mitigations at their proxy or WAF layer: block requests containing semicolons in URL paths to prevent the authentication bypass, and drop requests with Connection headers containing “X-Real-Ip” values to protect actuator endpoints.

These temporary measures can reduce exploitation risks while awaiting official patches.

The disclosure timeline began on February 13, 2025, with researchers providing full details to Versa.

Despite initial acknowledgment and promises of patches by April 7th, no fixes were delivered by the 90-day disclosure deadline on May 13th, 2025.