CVE-2026-41013: CloudFoundry Diego Privilege Escalation

CVE-2026-41013 Overview

CVE-2026-41013 is an input validation bypass in the SMB volume mount handling of Cloud Foundry Foundation's diego-release. A low-privileged Cloud Foundry space developer can smuggle arbitrary kernel CIFS mount options past the allowlist by abusing comma handling in tenant-controlled mount parameters. Successful exploitation enables privilege escalation and bypass of security controls on multi-tenant Diego cells. The flaw is classified under CWE-88: Improper Neutralization of Argument Delimiters in a Command.

Critical Impact
A tenant with space developer permissions can inject arbitrary CIFS mount options into the kernel mount syscall, breaking multi-tenant isolation on shared Diego cells.

Affected Products

Cloud Foundry smb-volume-release - all versions prior to v3.60.0
Cloud Foundry cf-deployment - all versions prior to v56.0.0
Cloud Foundry diego-release SMB volume mount component

Discovery Timeline

2026-06-01 - CVE-2026-41013 published to NVD
2026-06-02 - Last updated in NVD database

Technical Details for CVE-2026-41013

Vulnerability Analysis

The vulnerability resides in how the SMB volume service in diego-release constructs the option string passed to the kernel CIFS mount operation. Diego accepts mount parameters from tenant applications and validates them against an allowlist before invoking the mount. The allowlist check inspects individual option keys but does not account for comma characters embedded within tenant-supplied option values.

Because the Linux CIFS mount syntax uses commas as the option separator, an attacker who places a comma inside an otherwise-permitted value effectively appends additional options that were never reviewed by the allowlist. The kernel parses the smuggled options as first-class mount flags. This argument-delimiter neutralization failure is the defining behavior of [CWE-88].

The attack requires authenticated access as a CF space developer, which is a low-privilege role in a multi-tenant foundation. No user interaction is required, and the smuggled options execute with the privilege of the Diego cell's mount helper rather than the tenant.

Root Cause

The mount-option allowlist treats input as a structured key-value map but fails to escape, reject, or canonicalize comma characters in values before serializing the options back into a comma-delimited CIFS option string. The serialized string is handed to the kernel without a second-pass validation against the resulting flat option list.

Attack Vector

An attacker authenticates to the Cloud Foundry API as a space developer and binds an SMB volume service instance with a crafted parameter containing an embedded comma. When an application in the space is staged or restarted, the Diego cell invokes the SMB volume mount, the smuggled options reach the kernel CIFS client, and the attacker controls security-relevant mount flags such as those governing UID/GID mapping, file mode behavior, or credential handling on the shared cell.

No public proof-of-concept code is available. Refer to the Cloud Foundry advisory for the vendor's technical writeup.

Detection Methods for CVE-2026-41013

Indicators of Compromise

SMB volume service bindings whose mount_config or parameter values contain comma characters in unexpected fields such as username, share, or version.
mount.cifs invocations on Diego cells with option strings containing duplicated keys or options outside the documented Cloud Foundry allowlist.
Unexpected UID, GID, file_mode, dir_mode, or credentials arguments in kernel CIFS mount syscalls originating from the volume-mountd process.

Detection Strategies

Audit cf API logs for create-service-binding and bind-service calls targeting SMB volume services and flag parameter values containing commas.
Parse /var/vcap/sys/log/smbdriver/ and diego-cell logs for mount option strings, comparing the final option list against the documented allowlist.
Inspect /proc/mounts on Diego cells for CIFS mounts with options that were not requested by the platform operator.

Monitoring Recommendations

Forward Diego cell auditd records for the mount syscall to a centralized log store and alert on CIFS mounts containing non-allowlisted options.
Track version drift of smb-volume-release and cf-deployment across foundations to identify cells still running vulnerable releases.
Alert on space developer accounts that create or update SMB service bindings at an unusual rate.

How to Mitigate CVE-2026-41013

Immediate Actions Required

Upgrade smb-volume-release to v3.60.0 or later on every Diego cell that runs the SMB volume driver.
Upgrade cf-deployment to v56.0.0 or later to pull in the fixed component versions across the foundation.
Until the upgrade lands, disable the SMB volume service broker or remove the smbdriver job from Diego cells in untrusted multi-tenant environments.
Review existing SMB service bindings and unbind any whose parameters contain comma characters in non-list fields.

Patch Information

The Cloud Foundry Foundation has published fixed versions: smb-volume-release v3.60.0 and cf-deployment v56.0.0. Both releases tighten the mount-option allowlist so that comma-bearing tenant values are rejected or escaped before the option string is serialized for the kernel mount call. Details are documented in the Cloud Foundry advisory.

Workarounds

Restrict the space developer role in shared foundations and revoke SMB volume service access for spaces that do not require it.
Apply a custom policy on the service broker to reject any binding parameter value containing a comma.
Run SMB-dependent workloads on dedicated isolation segments so that smuggled mount options cannot affect other tenants.

bash

# Example: list SMB service bindings and flag parameter values containing commas
cf curl /v3/service_credential_bindings?service_instance_type=managed \
  | jq '.resources[] | select(.parameters | tostring | contains(","))'