CVE-2026-20093: Critical Cisco IMC Authentication Bypass Carries CVSS 9.8

CVE: CVE-2026-20093 Affected Product: Cisco Integrated Management Controller (IMC) CVSS Score: 9.8 (Critical)

Vulnerability Overview

Cisco has released security updates addressing a critical authentication bypass vulnerability in the Cisco Integrated Management Controller (IMC). Tracked as CVE-2026-20093, the flaw carries a CVSS v3 base score of 9.8 out of 10.0, placing it among the most severe vulnerability classes an enterprise product can carry.

The vulnerability allows an unauthenticated, remote attacker to bypass authentication controls and gain access to affected systems with elevated privileges. No credentials are required to exploit this flaw, and exploitation is achievable over the network without user interaction — characteristics that contribute directly to its near-maximum severity score.

Technical Description

Cisco IMC is the out-of-band server management interface embedded in Cisco UCS (Unified Computing System) servers and several other Cisco compute platforms. It provides administrators with remote access to hardware-level management functions — including power cycling, BIOS configuration, KVM console access, and firmware updates — independent of the host operating system.

The flaw is classified as an authentication bypass, meaning the underlying access control mechanism that enforces identity verification before granting administrative access can be circumvented. An attacker exploiting CVE-2026-20093 does not need to supply valid credentials. Once authentication is bypassed, the attacker operates with elevated privileges, giving them effective control over hardware management functions.

The attack vector is network-based, the attack complexity is low, no privileges are required, and no user interaction is needed. These four factors combine to produce the 9.8 CVSS score. The only reason this vulnerability does not achieve a perfect 10.0 is the absence of a confirmed impact on confidentiality, integrity, and availability at the absolute maximum scope level under the scoring rubric — though practical exploitation consequences are severe.

Real-World Impact

Compromise of the IMC interface gives an attacker hardware-level access to affected servers. From that position, an attacker can:

  • Modify BIOS and firmware settings, potentially persisting malware below the operating system level in a manner that survives reimaging.
  • Access the KVM console, giving full visibility into and control over the server's display, keyboard, and mouse — regardless of what the OS is doing.
  • Mount virtual media, allowing an attacker to boot the server from a remote ISO image and bypass OS-level controls entirely.
  • Power cycle or brick hardware, creating denial-of-service conditions against physical infrastructure.
  • Pivot into adjacent network segments, since IMC interfaces are often connected to dedicated out-of-band management networks that may themselves connect to other sensitive assets.

Organizations running Cisco UCS servers in data centers, colocation facilities, or private cloud environments are directly exposed. The risk is amplified anywhere the IMC interface is accessible from untrusted networks — a misconfiguration that is more common than it should be, particularly in environments where management interfaces share routing with production traffic.

Given the critical CVSS score and the network-accessible, zero-credential exploitation path, this vulnerability is a high-priority target for both opportunistic attackers conducting automated scanning and targeted intrusion operators seeking persistent, OS-independent footholds.

Affected Versions

Cisco has published a security advisory identifying the specific IMC software versions affected by CVE-2026-20093. Administrators should consult the official Cisco Security Advisory directly at tools.cisco.com/security/center to confirm whether their deployed versions fall within the vulnerable range. Cisco UCS C-Series, E-Series, and S-Series rack servers are among the product lines that use Cisco IMC and should be evaluated immediately.

Patching and Mitigation Guidance

1. Apply the patch immediately. Cisco has released fixed software versions. Administrators should upgrade IMC firmware to the corrected release identified in the Cisco security advisory. Treat this as an emergency change given the CVSS 9.8 score and zero-authentication exploitation path.

2. Restrict network access to the IMC interface. IMC management ports should never be reachable from untrusted or production networks. Place all out-of-band management interfaces — including IMC, IPMI, and iDRAC equivalents — on a dedicated, isolated management VLAN with strict ACLs. Allow access only from authorized jump hosts or management workstations.

3. Audit current IMC exposure. Run network scans against your management IP ranges to identify any IMC interfaces inadvertently exposed to broader network segments. Cisco IMC typically listens on TCP port 443 (HTTPS web UI) and TCP port 22 (SSH CLI). Confirm no interfaces are reachable from the internet or untrusted internal segments.

4. Review IMC access logs. Examine authentication logs on IMC interfaces for anomalous access attempts or successful sessions from unexpected source IPs. Correlate timestamps with other security telemetry from the same servers.

5. Enable multi-factor authentication where supported. Some IMC versions support LDAP integration and additional authentication controls. Enabling these does not substitute for patching but reduces exposure if an attacker finds another vector.

6. Monitor Cisco's advisory page for updates. Cisco may release additional details, including indicators of exploitation, as the advisory matures. Subscribe to Cisco PSIRT notifications at tools.cisco.com/security/center/psirtrss20ForSecurityAdvisories.xml.

References