Senior Software Engineer — Embedded C / Firewall Client

About the role

For more than 30 years, SonicWall has delivered a partner-first unified cybersecurity portfolio that helps SMBs, MSPs, and IT teams consolidate network security, endpoint security, security service edge (SSE), and threat response across hybrid environments. By bringing connected technology, real-time threat intelligence, automation, and expert services together, SonicWall helps organizations simplify security operations, achieve better security outcomes, and lower total cost of ownership. Backed by a global ecosystem of more than 17,000 partners, SonicWall delivers enterprise-grade protection built for SMB and mid-market realities.

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SonicWall is hiring a Senior Software Engineer to develop and maintain the Content Filtering Service client embedded in SonicOS — the firmware running on SonicWall firewall appliances worldwide. This module intercepts live traffic, queries the CFS rating servers in real time, and enforces URL-based content filtering policies at the packet level. This is security-critical code: a policy bug is a traffic bypass on a deployed security appliance.

The codebase is in C with a split Control Plane / Data Plane architecture, multi-blade cache synchronization, and multiple firmware version upgrade paths.

Responsibilities

• Maintain, harden, and extend the CFS client module across both the control plane and data plane.

• Own the binary UDP protocol implementation between the firewall and the CFS rating servers, ensuring correctness and compatibility across protocol versions.

• Develop and maintain complete IPv4 and IPv6 support across all code paths.

• Own the firmware upgrade and migration paths, ensuring they are atomic, failure-safe, and correctly handle all supported version transitions.

• Improve reliability of inter-blade cache synchronization on multi-blade appliances.

• Collaborate with the server-side on coordinated protocol changes.

• Document the concurrency model, upgrade invariants, and dataplane integration for long-term maintainability.

• Collaborate asynchronously with a US-based team and the India-based server team.

Requirements

• Expert-level C (not C++): disciplined manual memory management, pointer arithmetic, and systems design.

• Multi-core concurrency in C: reader-writer locks, spinlocks, atomic operations, and memory ordering.

• Kernel-level networking: deep understanding of how a packet moves through a firewall dataplane — TCP/UDP processing, flow cache, connection tracking. Userspace socket programming alone is not sufficient.

• Strong IPv4 and IPv6 across all code paths.

• Comfortable navigating and owning a large C codebase with multiple subsystems.

• Experience with network testing and debugging tools: packet capture (Wireshark/tcpdump), traffic generators, GDB.

• Good written English for remote, asynchronous collaboration.

Nice to have

• Experience with multi-blade or multi-ASIC hardware platforms (Octeon/CVMX or similar).

• Understanding of symmetric encryption (AES-CBC, DES) at the C implementation level.

• Prior experience on a security appliance, network device, or UTM firmware codebase.

• Familiarity with TLV binary protocol design and versioning.

• Experience with C fuzz testing or sanitizers (AFL, AddressSanitizer, ThreadSanitizer).

Education & Experience

At least 8 years of related experience with a Bachelor's degree; or 6 years with a Master's degree; or a PhD with 3 years' experience; or equivalent experience preferred. Degree in Computer Science, Engineering, or related field preferred.

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