# CVE-2026-61500 — rejetto hfs

> As of 2026-10-01, CVE-2026-61500 is a CRITICAL-severity vulnerability in rejetto hfs, CVSS v3.1 9.8, EPSS 0.9% (61.2th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-61500, most recently “Rejetto HTTP File Server (HFS) 3.x session forgery via predictable Math.random() signing key leads to unauthenticated admin access and RCE (CVE-2026-61500) under active exploitation”.

**Last updated:** 2026-10-01

## What is CVE-2026-61500?

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.

The record classifies CVE-2026-61500 under weakness class [CWE-338](https://cwe.mitre.org/data/definitions/338.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 102 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 9.8 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **CVSS v4.0 base score:** 9.3 (`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`)
- **EPSS (FIRST):** 0.9% probability of exploitation in the next 30 days, higher than 61.2% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 9.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-13, last modified 2026-10-01

## Is CVE-2026-61500 being exploited?

Weaponised exploit code for CVE-2026-61500 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 36 in the Threadlinqs vulnerability feed.

- [aramosf/CVE-2026-61500](https://github.com/aramosf/CVE-2026-61500) (github)

## Affected products and versions

- **rejetto**: hfs

## How to fix CVE-2026-61500

No vendor patch reference has been recorded for CVE-2026-61500 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-61500

1 tracked threat in the Threadlinqs corpus references CVE-2026-61500, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Rejetto HTTP File Server (HFS) 3.x session forgery via predictable Math.random() signing key leads to unauthenticated admin access and RCE (CVE-2026-61500) under active exploitation](https://intel.threadlinqs.com/threat/TL-2026-2865) — CRITICAL · 2026-10-03

## Sources

Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [github.com — release notes](https://github.com/rejetto/hfs/releases/tag/v3.2.1)

**Third-party advisory**

- [vulncheck.com — third party advisory](https://www.vulncheck.com/advisories/rejetto-hfs-session-forgery-via-predictable-signing-key)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-61500
Full detection coverage and IOCs for threats exploiting CVE-2026-61500 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp