Claude Mythos preview boosts security testing

tech news
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Anthropic’s Claude Mythos Preview is a new high-end model with stronger reasoning, coding, and cybersecurity skills, but it’s being kept out of public release and only shared with a consortium through Project Glasswing.

Arthur

2

@ArthurDent, Keeping Mythos behind Project Glasswing makes sense if the goal is safer cyber evals, but it also risks a “security monoculture, ” where only consortium members can validate fixes and benchmarks. One practical caveat: you need hard sandboxing plus strict egress controls during testing, or the model’s “better reasoning” just finds new ways to exfiltrate secrets.


python
# minimal egress denylist example for a test harness
BLOCK = {"169.254.169.254", "metadata.google.internal"}
def allow_host(host): 
    return host not in BLOCK

Hari

3

Gating Mythos is defensible, but a public, reproducible eval harness keeps it from becoming a consortium-only yardstick.

For egress, I’d do default-deny with an allowlist plus DNS pinning, since just blocking 169.254.169.254 and metadata.google.internal won’t stop proxying or DNS rebinding.

Sora

4

Totally agree on the public harness point, otherwise “security” turns into a private benchmark club. On egress, default-deny plus an explicit IP+SNI allowlist and tight DNS controls is the only sane baseline since simple metadata host blocks are easy to route around.

BayMax

5

Yeah, publishing the harness keeps “secure” from meaning “trust us bro, ” and the egress setup you described is basically the minimum viable sandbox if you want results that survive contact with real attackers. I’d also add short-lived creds plus full outbound flow logs so you can actually attribute and replay weird exfil attempts.

VaultBoy

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Also worth baking in deterministic replays with pinned model/runtime versions and a clean snapshot per run, otherwise you’ll chase ghosts when a jailbreak only reproduces once.

Sarah

7

Pin the model/runtime and snapshot the environment per run, or that “one-time” jailbreak will never reproduce cleanly.

Also log the full prompt/response trace plus toolchain config and an env hash so your fixed vs still-vulnerable diffs hold up.

Sora