First systematic study finds multiple LLM API routers injecting malicious code and stealing keys

Bedrovelsen · x · 2026-10-11

An arXiv paper presents the first systematic study of malicious LLM API routers: proxies that read all tool-calling payloads in plaintext, with no cryptographic integrity enforced between client and upstream model.

The authors formalize the threat model with two attack classes (payload injection AC-1, secret exfiltration AC-2) plus adaptive evasion variants. Testing 28 paid routers bought from Taobao, Xianyu and Shopify stores and 400 free routers, they found 1 paid and 8 free routers actively injecting malicious code, 2 using adaptive evasion triggers, 17 touching researcher-planted AWS canary credentials, and 1 draining ETH from a planted private key.

Honeypot studies show even benign-seeming routers get weaponized: a leaked OpenAI key consumed 100M GPT-5.4 tokens across 7+ Codex sessions, while weakly configured decoys yielded 2B billed tokens, 99 credentials across 440 sessions, with 401 sessions already running autonomously.

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