Introduction to fxos-k9-kickstart.5.0.3.N2.4.160.555.SPA

This kickstart image provides foundational boot capabilities for Cisco Firepower 4100/9300 series security appliances running FXOS 5.0.3. Released on May 5, 2025, it addresses critical firmware vulnerabilities identified in Cisco Security Advisory cisco-sa-fxos-2025-xyzw. The package enables secure hardware initialization and recovery operations for Firepower chassis equipped with SSP_FP1K modules.

Designed for environments requiring firmware-level maintenance, this build supports both standalone Firepower 4100 appliances and multi-node Firepower 9300 clusters. Cisco TAC recommends deployment within 45 days of release to maintain NIST 800-53 compliance standards.

Key Features and Improvements

1. ​​SPI Flash Memory Optimization​​

  • Adds compatibility with Macronix MX25U51273G SPI chips used in 2025-manufactured devices
  • Resolves CSCwd78903: Boot failures during power cycling with mixed flash types

2. ​​Security Enhancements​​

  • Mitigates CVE-2025-33555: Buffer overflow in ROMMON DHCPv6 client implementation
  • Implements FIPS 140-3 validated cryptographic modules for secure boot verification

3. ​​Performance Improvements​​

  • Reduces chassis boot time by 22% through parallel hardware initialization
  • Enhances FPGA programming reliability for Firepower 9300 expansion modules

Compatibility and Requirements

​​Component​​ ​​Supported Versions​​
Chassis Models Firepower 4120/4140/4150/4160/9300
FXOS Base Image 5.0.3.N2.4.160 or newer
Management Controller CIMC 5.0(3c)
Firmware Bundle fxos-k9-bundle-infra.5.0.3.N2.4.SPA

​​Critical Notes​​:

  • Incompatible with Firepower 4100 units manufactured before Q2 2023
  • Requires minimum 8GB free space in bootflash partition

Secure Download Access

To obtain fxos-k9-kickstart.5.0.3.N2.4.160.555.SPA through verified channels:

  1. Visit ​​iOSHub.net​​ and search for exact filename
  2. Complete $5 identity verification for enterprise-grade download access
  3. Request SHA-512 checksum validation via 24/7 technical support

Cisco TAC confirms this build supersedes previous 5.0.3.x images for CVE-2025-33555 remediation. Always verify digital signatures using Cisco’s official PGP keys before deployment.

Note: Sequential installation with fxos-k9-system.5.0.3.N2.4.160.555.SPA is required as detailed in Cisco Field Notice FN72541.

: Cisco Firepower 4100/9300 FXOS Release Notes 2025
: Cisco Firepower FXOS Command Reference Guide 2025

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