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Anatomy of an SMS firewall evasion attempt.

A walkthrough of how grey-route operators try to bypass firewalls — and how modern ML-based detection catches them anyway.

BroadNet Operator Solutions
AuthorEditorial standards
8 min read
Operators · Issue 11
8 min read

rey-route operators have a multi-year arms race against firewall vendors. Here's a typical evasion playbook seen at a MENA operator we work with — and how the firewall caught each step.

Step 1 — sender ID rotation

Attacker registers 50+ sender IDs across 12 fake business identities. Each is used for ~10,000 messages before being retired. Pre-ML firewalls miss this entirely; rule engines can't list every variant. Behavioural ML catches it within 6 hours: the throughput pattern, content fingerprint, and recipient overlap signal correlated activity across the sender IDs.

Step 2 — content variation

Attacker template-injects random characters to avoid content-hash deduplication. The firewall switches to MinHash + n-gram similarity, identifying the underlying template through the noise.

Step 3 — route rotation

Attacker switches between three foreign aggregators per hour. The firewall correlates by destination MSISDN pattern (a known list of customers being phished) and blocks at recipient pattern, not source.

Lesson

Rule engines alone can't keep up. Behavioural ML can — provided it's trained on operator-specific data, not generic CPaaS data. This is one of the reasons BroadNet's firewall, trained on MENA operator traffic since 2003, has a measurable edge over global-firewall vendors retrofitting to the region.

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BroadNet Operator Solutions

Operator Solutions builds and runs SMS firewalls, SS7 protection, and revenue assurance for mobile operators. They have been doing it on MENA networks since 2003. They write about what they see.

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