CVE-2026-41013: Cloud Foundry Diego SMB Mount Input Validation Bypass (CVSS 8.1)

Technical summary

CVE-2026-41013 is an input validation bypass vulnerability in the SMB volume mount handling logic within CloudFoundry Foundation's diego-release. The vulnerability exists in smb-volume-release and CF Deployment, where the mount-option allowlist enforcement is insufficient. An authenticated low-privileged CF space developer can craft malformed input to inject arbitrary CIFS mount options, bypassing the intended security controls. The CVSS 3.1 score of 8.1 (HIGH) reflects the combination of network accessibility, low attack complexity, low privilege requirements, high confidentiality and integrity impact, and absence of availability impact. CWE-88 (Improper Neutralization of Argument Delimiters in a Command) is the primary weakness enabling this bypass.

Business impact

In multi-tenant Cloud Foundry deployments, this vulnerability poses a significant risk to isolation guarantees. A developer in one space could potentially access or modify data belonging to other tenants on the same Diego cell, or escalate their own privileges to perform administrative actions. For organizations using CF as a shared platform service, this breaks the fundamental trust boundary between teams and could lead to unauthorized data exposure, modification of production workloads, or circumvention of compliance controls.

Affected systems

All versions of smb-volume-release prior to v3.60.0 are vulnerable. Additionally, CF Deployment versions prior to v56.0.0 are affected. Organizations should verify which versions are deployed in their environment. Systems using NFS or other non-SMB volume mounts may not be directly affected by this particular vulnerability, though they should be evaluated separately.

Exploitability

This vulnerability requires CF space developer credentials—a low privilege level in Cloud Foundry's role-based access model. No special network access or user interaction is needed; exploitation is straightforward once a developer has legitimate access to the platform. The attack surface is high in multi-tenant environments where numerous developers have platform access. The fact that this has not been added to CISA's Known Exploited Vulnerabilities list does not mean exploitation is not occurring; vigilant monitoring is warranted.

Remediation

Patch smb-volume-release to v3.60.0 or later, and upgrade CF Deployment to v56.0.0 or later. Patches should be applied to all Diego cells and associated components. Verify the patched versions through deployment manifests and cf cli commands. Organizations unable to patch immediately should consider restricting SMB volume mount usage via policy and monitoring mount option injection attempts in logs.

Patch guidance

Deploy smb-volume-release v3.60.0 or newer. Simultaneously update CF Deployment to v56.0.0 or later to ensure consistency. Patch deployment should be coordinated to minimize disruption to running applications. After patching, verify that SMB volume mounts function correctly for legitimate use cases and validate that the allowlist enforcement is working as intended. Test in a non-production environment first if possible.

Detection guidance

Monitor CF logs and Diego cell logs for suspicious SMB mount operations, particularly mount options that differ from your organization's standard configuration. Watch for developers attempting to mount with kernel-level CIFS options outside the expected allowlist. Network-based detection should focus on unusual SMB negotiation patterns or mount requests containing shell metacharacters or escape sequences. Host-level monitoring of /proc/mounts or cifs-related system calls on Diego cells may reveal injection attempts.

Why prioritize this

The combination of HIGH CVSS score, low barrier to exploitation (requires only developer credentials), and multi-tenant isolation impact makes this a priority for rapid patching. However, it is not on the KEV list, suggesting it may not yet be widely exploited in the wild. Organizations should prioritize this for patching within their standard update cycle but should not delay other critical work if patch testing requires time.

Risk score, explained

The CVSS 3.1 score of 8.1 reflects: network-accessible attack vector, low attack complexity (standard input validation bypass techniques), requirement for low privilege (CF space developer role), high impact to confidentiality and integrity (ability to access other tenants' data and escalate privileges), no availability impact, and unchanged scope. This score appropriately captures the severity in a multi-tenant context; single-tenant deployments may face lower practical risk if inter-team isolation is not a concern.

Frequently asked questions