CVE-2025-20261: Cisco IMC Privilege Escalation Vulnerability

CVE-2025-20261 Overview

CVE-2025-20261 is a privilege escalation vulnerability in the Secure Shell (SSH) connection handling of Cisco Integrated Management Controller (IMC) for Cisco UCS B-Series, UCS C-Series, UCS S-Series, and UCS X-Series Servers. An authenticated, remote attacker with a valid user account can use crafted syntax during SSH connection to access internal services with elevated privileges. Successful exploitation allows unauthorized system modifications, including the creation of new administrator accounts on the affected device. The vulnerability is tracked under [CWE-923] (Improper Restriction of Communication Channel to Intended Endpoints).

Critical Impact

An authenticated attacker can escalate privileges through SSH and create new administrator accounts on Cisco UCS server management controllers.

Affected Products

• Cisco UCS B-Series Servers (Integrated Management Controller)
• Cisco UCS C-Series and UCS S-Series Servers (Integrated Management Controller)
• Cisco UCS X-Series Servers (Integrated Management Controller)

Discovery Timeline

• 2025-06-04 - CVE-2025-20261 published to the National Vulnerability Database (NVD)
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-20261

Vulnerability Analysis

The vulnerability resides in the SSH connection handling logic of the Cisco IMC, the dedicated out-of-band management processor embedded in Cisco UCS servers. The IMC exposes administrative interfaces over SSH for hardware management, firmware operations, and console access. An attacker authenticated with a low-privilege account can supply crafted syntax during the SSH session to reach internal services that should remain restricted to higher-privileged contexts.

The flaw enables vertical privilege escalation. Once the attacker reaches the exposed internal services, they gain the ability to modify system state, alter configuration, and provision new accounts with administrator privileges. Because the IMC controls server power state, firmware, virtual media, and console redirection, compromise at this layer extends below the host operating system and persists across OS reinstalls.

Root Cause

The root cause is insufficient restriction on access to internal services exposed through the SSH channel. The IMC fails to properly enforce authorization boundaries between the authenticated SSH session context and the internal service endpoints it can reach. The weakness is classified under [CWE-923] as an improper restriction of communication channel to intended endpoints.

Attack Vector

Exploitation requires network reachability to the IMC SSH service and a valid local user account. The attacker initiates an SSH connection to the management interface and submits crafted command syntax during the session. The crafted input bypasses access controls and delivers the attacker into internal service contexts that operate with elevated privileges. No user interaction beyond the attacker's own authentication is required. Refer to the Cisco Security Advisory for vendor-confirmed technical details.

Detection Methods for CVE-2025-20261

Indicators of Compromise

• Unexpected SSH sessions to Cisco IMC management interfaces from unusual source addresses or at unusual times.
• New administrator accounts appearing in IMC local user databases without an authorized change request.
• IMC audit log entries showing privilege changes, role assignments, or account creation following SSH login events.
• Configuration changes to IMC services (virtual media, KVM, IPMI) immediately following an SSH session from a low-privilege user account.

Detection Strategies

• Compare current IMC user account inventories against an authoritative baseline and alert on additions or role changes.
• Correlate IMC SSH authentication events with subsequent privileged operations performed by the same session.
• Forward IMC syslog and audit data to a centralized analytics platform and create rules for low-privileged users invoking administrative actions.

Monitoring Recommendations

• Restrict IMC management network access to a dedicated administrative VLAN and monitor that segment for unauthorized connection attempts.
• Enable and retain Cisco IMC audit logging, including SSH session command history, and ship logs to a SIEM for retention beyond local device storage.
• Alert on any IMC firmware, user, or role configuration change outside scheduled maintenance windows.

How to Mitigate CVE-2025-20261

Immediate Actions Required

• Apply the fixed Cisco IMC firmware version identified in the Cisco Security Advisory for each UCS B-Series, C-Series, S-Series, and X-Series platform.
• Audit all IMC local user accounts and remove accounts that are unused, shared, or unaccounted for.
• Rotate credentials for all remaining IMC accounts and enforce strong password policy.
• Restrict SSH access to the IMC to authorized management hosts only via access control lists or network segmentation.

Patch Information

Cisco has released fixed firmware addressing CVE-2025-20261. Customers should consult the Cisco Security Advisory to identify the fixed release applicable to each server model and IMC firmware train, then schedule upgrades through standard Cisco UCS firmware update procedures.

Workarounds

• No vendor-confirmed workaround fully eliminates the vulnerability; patching is the supported remediation path.
• Reduce exposure by placing the IMC management interface on an isolated out-of-band network reachable only by trusted administrators.
• Limit which user accounts are provisioned on the IMC and apply the principle of least privilege to all remaining accounts.
• Disable SSH on the IMC where management is performed exclusively through other supported channels, if operationally feasible.

# Example: restrict IMC SSH access using a management ACL
# (apply via Cisco IMC CLI or Cisco UCS Manager policy)
scope cimc
  scope network
    set ssh-port 22
    create ssh-access-list <trusted-mgmt-subnet>/<prefix>
    commit