How to Fix CVE-2023-20079: Stack-based Buffer Overflow in Cisco IP Phones with Multiplatform Firmware

What is CVE-2023-20079?

Multiple vulnerabilities in the web-based management interface of certain Cisco IP Phones could allow an unauthenticated, remote attacker to execute arbitrary code or cause a denial of service (DoS) condition. For more information about these vulnerabilities, see the Details section of this advisory.

In short, a successful attacker gets remote code execution on the affected system. No confirmed in-the-wild exploitation is listed in CISA KEV at the time of writing, but the CVSS rating still warrants prompt patching.

Am I affected?

Check whether you run Cisco IP Phones with Multiplatform Firmware in your environment, then compare your installed version against the Affected row above.

show version

How to fix CVE-2023-20079

1. Read the official vendor advisory linked at the bottom of this page and identify the exact patched build for your release train.
2. Download the patched build of Cisco IP Phones with Multiplatform Firmware from the vendor's support portal. Use only signed images from the vendor.
3. Back up configuration and, where supported, take a snapshot of the host or appliance before you start.
4. Apply the update following the vendor's documented procedure. For clustered or high-availability deployments, patch the standby node first, fail over, then patch the previously active node.
5. Restart the affected service or appliance if the upgrade procedure requires it.
6. Re-run the version check from the previous section and confirm the build matches the fixed release.

Upgrade the affected Cisco platform

! Verify the running release on the device
show version
show inventory

! Stage the patched image from the Cisco Security Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ip-phone-cmd-inj-KMFynVcP
copy tftp://<fileserver>/<patched-image>.bin flash:

! Set the boot image and reload in a maintenance window
configure terminal
boot system flash:<patched-image>.bin
end
write memory
reload

! After reload, confirm the new image is running
show version | include image

Verify the fix landed

# 1. Confirm the running version matches the fixed-in version from the advisory:
#    https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ip-phone-cmd-inj-KMFynVcP
#    Use the platform-specific version probe above.

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag CVE-2023-20079 on the patched target.

# 3. Inspect recent service / kernel logs for crash loops or rollback events.
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

If you can't patch immediately

If patching has to wait, block external access to the affected service at the firewall and restrict to a small, audited management network. Enable any vendor-recommended detection rules or WAF signatures listed in the advisory. None of these are a substitute for the patch.

How to verify the fix worked

Confirm the running build of Cisco IP Phones with Multiplatform Firmware matches the fixed version listed by the vendor. Re-run any vulnerability scanner you used previously and confirm the finding for CVE-2023-20079 has cleared. Where the vendor publishes a detection rule or IOCs, sweep your logs for evidence of pre-patch exploitation.

Why this CVE matters

CVSS 9.8 (Critical) reflects either remote, unauthenticated exploitability, full impact on confidentiality / integrity / availability, or both. Most internal SLAs map a Critical rating to a 7-to-15 day patch deadline regardless of in-the-wild reports. Public-facing instances should be patched on the shorter end of that window.

Monitoring and detection

After you apply the patch, treat the affected component as a known-good baseline and watch for regression. Concrete steps:

• Re-run your usual vulnerability scanner on a weekly cycle for the next month and confirm the finding stays clear.
• Forward the affected component's logs to your SIEM, then write a rule for any failed-auth burst or unusual configuration change on the component.
• If the vendor advisory lists indicators of compromise, hash patterns, or specific log strings, build detection rules in your SIEM around them and back-search the last 90 days of logs.
• Tag the patched build in your CMDB so future audits can confirm it stayed patched through any rebuild or re-image.

Defensive hardening beyond the patch

Patching closes this specific CVE. A few common-sense controls reduce the blast radius of the next one in the same component:

• Restrict management interface (HTTPS / SSH) access to a small administrative subnet using interface ACLs or trusted-host lists.
• Enable AAA logging and forward to your SIEM. Alert on any successful admin login from outside the trusted subnet.
• Where the vendor supports it, enable two-factor authentication for admin accounts.
• Schedule quarterly password rotation for any local admin or break-glass accounts on the appliance.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2023-20101: Use of Hard-coded Credentials in Cisco Emergency Responder — Use of Hard-coded Credentials in Cisco Emergency Responder
• How to Fix CVE-2023-20032: Buffer Copy without Checking Size of Input in Cisco Secure Web Appliance — Buffer Copy without Checking Size of Input in Cisco Secure Web Appliance
• How to Fix CVE-2023-20048: Improper Privilege Management in Cisco Firepower Management Center , Improper Privilege Management in Cisco Firepower Management Center
• How to Fix CVE-2023-20118: Command Injection in Cisco Small Business RV Series Router Firmware , Command Injection in Cisco Small Business RV Series Router Firmware
• How to Fix CVE-2023-20269: Authentication Bypass in Cisco Cisco Adaptive Security Appliance (ASA) Software , Authentication Bypass in Cisco Cisco Adaptive Security Appliance (ASA) Software

Is CVE-2023-20079 being actively exploited?

Not at the time of writing. It is not listed in CISA's Known Exploited Vulnerabilities catalog. That can change, so monitor the advisory and KEV catalog.

How severe is CVE-2023-20079?

CVSS rates it 9.8 (Critical). Treat it accordingly in your prioritisation queue.

Do I have to take Cisco IP Phones with Multiplatform Firmware offline to apply the patch?

That depends on your deployment topology. For high-availability or clustered setups you can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.

References

• Official vendor advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ip-phone-cmd-inj-KMFynVcP
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-20079
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

*Written by Sai Kiran Pandrala on 2026-05-25. Sourced from the official vendor advisory, the NVD record, and the CISA KEV listing. Always confirm against the vendor's advisory before applying changes in production.*