Detections
Analytics

CVE-2026-61500

critical

Description

Rejetto HFS 3.0.0 through 3.2.0 derives its session-cookie signing key from the non-cryptographic Math.random() generator and discloses outputs of the same generator to unauthenticated clients during login. A remote attacker can collect a small number of login responses, reconstruct the generator's state, recover the signing key, and forge a valid administrator session cookie, leading to full administrative access and remote code execution via the server_code configuration feature.

References

https://thehackernews.com/2026/10/anthropic-expands-claude-access-for.html

https://www.securityweek.com/exploitation-hits-rejetto-hfs-vulnerability-discovered-by-ai/

https://www.bleepingcomputer.com/news/security/rejetto-hfs-servers-now-actively-scanned-for-critical-rce-flaw/

https://thehackernews.com/2026/10/attackers-target-rejetto-hfs-flaw-that.html

https://securityaffairs.com/200444/ai/anthropic-mythos-found-a-bug-in-rejetto-hfs-attackers-are-now-exploiting-it.html

https://www.theregister.com/security/2026/10/03/anthropics-super-bug-hunting-model-mythos-is-hardcore-good-at-math-as-latest-vuln-under-attack-shows/5300933

https://www.vulncheck.com/advisories/rejetto-hfs-session-forgery-via-predictable-signing-key

https://github.com/rejetto/hfs/releases/tag/v3.2.1

https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-43505

Details

Source: Mitre, NVD

Published: 2026-07-13

Updated: 2026-07-15

Risk Information

CVSS v2

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Severity: Critical

CVSS v3

Base Score: 9.8

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity: Critical

CVSS v4

Base Score: 9.3

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Severity: Critical

EPSS

EPSS: 0.00987

Vulnerability Watch

Tenable Research has classified this CVE under the following Vulnerability Watch classification, which includes active and historical (inactive) classifications. You can learn more about these classifications on our blog.

Vulnerability Being Monitored