Executive brief
Rejetto HFS, a popular file-sharing server, contains a security flaw in how it secures user sessions. An attacker can predict the secret keys used to sign login cookies by observing a few login attempts. This allows an unauthorized person to impersonate an administrator, take full control of the server, and execute malicious code, potentially leading to a complete system takeover and data theft.
Technical details
Rejetto HFS (versions 3.0.0 to 3.2.0) utilizes the non-cryptographic Math.random() generator to derive its session-cookie signing key. Because the application also discloses outputs from this same generator to unauthenticated clients during the login process, a remote attacker can collect a small number of responses to reconstruct the PRNG state. Once the state is known, the attacker can recover the signing key and forge a valid administrator session cookie. With administrative access, the attacker can leverage the 'server_code' configuration feature to achieve remote code execution (RCE). The vulnerability is addressed in version 3.2.1.
Affected products
- Rejetto HFS (HTTP File Server) 3.0.0 through 3.2.0
Timeline
- 2026-07-13: disclosed
- 2026-07-13: patched: Fixed in version 3.2.1
- 2026-07-13: advisory