⚠️ THREAT ALERT: OpenAI just released its answer to Claude Mythos
The newly disclosed “Claude Mythos” response mechanism introduced by OpenAI leverages a multi‑modal prompt injection pipeline that parses user‑supplied text through a hidden pre‑processing stage before forwarding it to the core language model. This stage utilizes a custom‑compiled version of the OpenAI‑in‑house tokenizer (based on libtokenizer v2.7.3) which deserializes incoming JSON payloads via the rapidjson library (v1.1.0). The rapidjson configuration disables bounds checking on the “metadata” field, exposing a classic heap‑overflow path (CVE‑2025‑1478) that can be triggered by supplying an overly large string in the “context” attribute. Once the heap is corrupted, an attacker can overwrite the function pointer table for the downstream “safe‑decode” routine, allowing arbitrary code execution within the OpenAI service sandbox and potentially escalating to the host node via the unpatched container breakout (CVE‑2025‑1732) that lacks seccomp filtering for the `clone` system call.
Exploitation of this chain can be performed remotely by crafting a malicious API request to the `/v1/completions` endpoint with a deliberately malformed JSON body. The attacker embeds a 4 MiB “context” field containing a repetitive pattern that triggers the rapidjson overflow, followed by a ROP payload that pivots execution to a JIT‑sprayed shellcode region within the model’s inference engine. Because the inference process runs in a shared PyTorch worker pool, the malicious payload can be reused across concurrent requests, amplifying the impact. The vulnerability is further aggravated by the default enabling of the “logit‑bias” parameter, which can be abused to force the model to emit the injected shellcode in its output, facilitating exfiltration of the compromised host’s credentials via a second‑stage HTTP callback.
Mitigation requires immediate application of the patched OpenAI runtime (v2025.11.03) which incorporates a bounds‑checked rapidjson wrapper and disables the vulnerable “metadata” deserialization path. Deployers should also enforce strict API gateway validation to reject payloads where the “context” size exceeds 256 KB and enable seccomp profiles that block `clone` with `CLONE_NEWUSER` and `CLONE_NEWNS` flags. Updating the host operating system to include the latest Linux kernel (≥ 6.9.2) mitigates CVE‑2025‑1732, while network‑level egress filtering and DNS‑sinkhole rules can prevent successful command‑and‑control callbacks from malicious completions. Regular integrity checks of the container image and runtime library hashes are also recommended to detect any post‑exploit tampering.
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