CVE-2026-61500 (VulnCheck/NVD; published mid-July 2026; GHSA-xxrm-3f86-v97j): Rejetto HTTP File Server (HFS) 3.0.0 through 3.2.0 derives the Koa/keygrip session-cookie signing key from non-cryptographic Math.random() and leaks outputs of the same V8 xorshift128+ PRNG to clients during loginSrp1. A remote attacker can collect a small number of login responses, reconstruct PRNG state, recover the signing key, forge an administrator session cookie, and reach RCE via the server_code / administrative API custom-endpoint path.

CVSS 3.1 9.8 Critical and CVSS 4.0 9.3 Critical (VulnCheck via NVD/CVE.report). Fixed in HFS 3.2.1 (GitHub release / commit).

UPDATE / desk hook 30 Sep 2026: Horizon3 Attack Research details how Anthropic Mythos (with a custom harness) rediscovered and fully chained the issue — including Z3-based PRNG state recovery and a working exploit path — as an agentic vulnerability-research case study. Primary: GHSA / rejetto v3.2.1; research wire: Horizon3 30 Sep.

UPDATE 5 Oct: VulnCheck (Patrick Garrity) says exploitation attempts began on 1 Oct 2026, a day after the Horizon3 write-up, from an unnamed China-based actor targeting real vulnerable hosts in the US; a public Python proof-of-concept by researcher Alejandro Ramos (aramosf) appeared in late September. It is the second Rejetto HFS flaw exploited in the wild after CVE-2024-23692 (2024).

No Australian exploitation reports so far. Wire: The Hacker News 5 Oct. SecurityWeek (5 Oct) adds that VulnCheck's 2 Oct warning described small-scale reconnaissance from a China Telecom IP address that hit VulnCheck canary hosts in Japan as well as the US. BleepingComputer (5 Oct) quotes VulnCheck VP of Security Research Caitlin Condon confirming the honeypot probes; VulnCheck has not reported successful exploitation or post-exploitation activity, and users are advised to move to 3.2.1 or, ideally, the latest stable release 3.3.4.