Source note · Troubleshooting Cisco IP phones stuck upgrading firmware
A phone with no CTL or ITL file (or a blank ITL because of Prepare Cluster for Rollback to Pre 8.0) blindly trusts the next CTL or ITL it downloads and uses that signer from then on.
Checked 2026-10-02
- Vendor
- Cisco
- Product
- Cisco Unified Communications Manager
- Subsystem
- ITL trust
- Deployment
- on-premises
- Region
- not restricted
- Release range
- 8.0 and later
- Checked
- 2026-10-02
Sources
- Understand CUCM Security By Default and ITL Operation and Troubleshooting — Cisco Systems · tier 2 current vendor documentation · ITL file and phone trust behaviour (no CTL/ITL present case)
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting Cisco IP phones stuck upgrading firmware: source note cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust. WarmTransfer. https://warmtransfer.net/knowledge/claims/cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust
BibTeX
@misc{warmtransfer-claim-cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust,
title = {Troubleshooting Cisco IP phones stuck upgrading firmware: source note cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust},
note = {Source note cucm-phone-firmware-upgrade-troubleshooting-itl-blind-trust, checked 2026-10-02}
}