CVE-2025-2312: cifs-utils Information Disclosure Flaw

CVE-2025-2312 Overview

A flaw was found in cifs-utils where the cifs.upcall program makes an upcall to the wrong namespace when attempting to obtain Kerberos credentials in containerized environments. This namespace confusion vulnerability allows containers to potentially access the host's Kerberos credentials cache, leading to sensitive credential disclosure.

Critical Impact

This vulnerability enables containers to escape their credential isolation boundary and access host Kerberos credentials, potentially allowing lateral movement or unauthorized access to network resources authenticated via Kerberos.

Affected Products

• cifs-utils package (versions prior to security patch)
• Linux systems using CIFS/SMB mounts with Kerberos authentication
• Containerized environments utilizing cifs-utils for network file system access

Discovery Timeline

• 2025-03-25 - CVE CVE-2025-2312 published to NVD
• 2025-03-27 - Last updated in NVD database

Technical Details for CVE-2025-2312

Vulnerability Analysis

This vulnerability is classified under CWE-488 (Exposure of Data Element to Wrong Session), which describes a condition where data intended for one session or context is incorrectly exposed to another. In the case of CVE-2025-2312, the cifs.upcall helper program fails to properly handle Linux namespace boundaries when retrieving Kerberos credentials.

When a CIFS mount requires Kerberos authentication, the kernel triggers an upcall to the userspace cifs.upcall program. In containerized environments, this upcall mechanism should respect namespace isolation to ensure that containers only access their own credential caches. However, due to improper namespace handling, the upcall targets the host's namespace instead of the container's namespace, exposing the host's Kerberos credential cache to containerized processes.

The local attack vector requires an attacker to have access to a container on the affected system, but the scope is changed (S:C) because the vulnerability crosses the container boundary to impact the host system's credentials.

Root Cause

The root cause lies in the namespace handling logic within cifs.upcall. When the program performs credential lookup operations, it fails to properly switch to or validate the calling process's namespace context. This results in the credential lookup occurring in the host's namespace rather than the container's namespace, regardless of where the triggering mount request originated.

The fix involves ensuring proper namespace awareness in the upcall mechanism so that Kerberos credential retrieval respects container isolation boundaries. Patches have been committed to both the cifs-utils repository and the Linux kernel SMB subsystem.

Attack Vector

An attacker with access to a container on a vulnerable system could trigger CIFS mount operations with Kerberos authentication. Due to the namespace confusion, the cifs.upcall program would access the host's Kerberos credential cache instead of a container-local cache. This could expose service tickets, TGTs (Ticket Granting Tickets), or other sensitive Kerberos credentials that the host system has cached.

The attack scenario requires:

1. A containerized environment running on a system with cifs-utils installed
2. The host system having active Kerberos credentials cached
3. The ability to trigger CIFS mount operations from within a container

Rather than demonstrating synthetic exploit code, the vulnerability mechanism involves the upcall namespace targeting logic. For technical implementation details, refer to the Samba CIFS Utils Commit and the Linux Kernel SMB Commit.

Detection Methods for CVE-2025-2312

Indicators of Compromise

• Unexpected cifs.upcall executions originating from containerized processes
• Container processes accessing /tmp/krb5cc_* or other credential cache files outside their namespace
• Anomalous CIFS mount attempts from containers that should not require Kerberos authentication
• Audit logs showing credential cache access patterns inconsistent with normal container operations

Detection Strategies

• Monitor cifs.upcall invocations and correlate with the originating namespace to identify cross-namespace credential access
• Implement container runtime security monitoring to detect attempts to access host Kerberos credential caches
• Use auditd rules to track access to Kerberos credential cache files (/tmp/krb5cc_*, /var/tmp/krb5cc_*)
• Deploy SentinelOne Singularity for real-time detection of container escape behaviors and unauthorized credential access

Monitoring Recommendations

• Enable kernel audit logging for CIFS-related syscalls and upcall mechanisms
• Monitor container orchestration platforms for containers attempting CIFS mounts with Kerberos
• Implement file integrity monitoring on host Kerberos credential cache locations
• Configure alerting for any cross-namespace credential access attempts

How to Mitigate CVE-2025-2312

Immediate Actions Required

• Update cifs-utils to the patched version containing commit 89b679228cc1be9739d54203d28289b03352c174
• Apply the Linux kernel SMB subsystem patch (commit db363b0a1d9e6b9dc556296f1b1007aeb496a8cf)
• Audit container configurations to identify those using CIFS mounts with Kerberos authentication
• Consider restricting container capabilities to prevent CIFS mount operations until patches are applied

Patch Information

Security patches have been committed to address this namespace handling issue. The Samba CIFS Utils Commit addresses the userspace component, while the Linux Kernel SMB Commit addresses kernel-level handling. Organizations should apply both patches and update their cifs-utils packages through their distribution's package manager once updated packages are available.

Workarounds

• Disable Kerberos authentication for CIFS mounts in containerized environments until patches are applied
• Use alternative authentication mechanisms (NTLM) for container CIFS mounts where security requirements permit
• Implement container security policies to block cifs.upcall execution from within containers
• Isolate containers requiring CIFS access onto dedicated hosts without cached Kerberos credentials

# Restrict cifs.upcall execution in containers using AppArmor
# Add to container AppArmor profile:
deny /usr/sbin/cifs.upcall x,

# Or using seccomp to restrict keyctl syscalls used by cifs.upcall
# Example seccomp profile addition (JSON):
# {"names": ["request_key", "keyctl"], "action": "SCMP_ACT_ERRNO"}