---
id: CVE-2026-78551
title: >-
  RansomLook contains multiple weaknesses in its authentication endpoint that
  allow an unauthenticated remote attacker to enumerate valid usernames, perform
  unrestricted password-guessing attacks, and potentially exhaust application
  worker…
summary: >-
  RansomLook contains multiple weaknesses in its authentication endpoint that
  allow an unauthenticated remote attacker to enumerate valid usernames, perform
  unrestricted password-guessing attacks, and potentially exhaust application
  worker…
severity: none
cwe:
  - CWE-307
  - CWE-400
published: '2026-08-24'
updated: '2026-10-12'
sourceUpdated: '2026-10-12T21:10:00.227'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78551'
references:
  - url: >-
      https://github.com/RansomLook/RansomLook/commit/8602740347b0e928ad9fbaf5bc6ff242337dec6b
    label: 5a6e4751-2f3f-4070-9419-94fb35b644e8
tags:
  - nvd
epss: 0.00649
epssPercentile: 0.49656
ingestedAt: '2026-10-12T22:05:40.343Z'
---

## Overview

RansomLook contains multiple weaknesses in its authentication endpoint that allow an unauthenticated remote attacker to enumerate valid usernames, perform unrestricted password-guessing attacks, and potentially exhaust application worker resources.

For local authentication, the login implementation previously checked whether a submitted username existed before invoking the password hash verification function. Requests containing a nonexistent username therefore returned significantly faster than requests for valid accounts, for which the computationally expensive password verification routine was executed. A remote attacker could measure these response-time differences to determine which usernames correspond to valid RansomLook accounts.

In addition, the /login endpoint did not restrict the number or frequency of failed authentication attempts. An attacker could consequently perform password brute-force, dictionary, password-spraying, or credential-stuffing attacks against known accounts without server-side throttling. For valid usernames, each authentication attempt also invokes the password key-derivation function, which consumes a significant amount of CPU time. A sufficiently high rate of login attempts could therefore occupy the application's synchronous Gunicorn workers and cause a denial of service affecting the entire application.

The issue has been addressed by always performing password verification using a randomly generated dummy password hash when the supplied username does not exist, eliminating the username-dependent timing discrepancy. Failed authentication attempts are additionally rate-limited per client IP address using Valkey/Redis, with five failed attempts within five minutes resulting in a one-hour block. The reverse-proxy configuration was also updated so that the application derives the client address from a trusted X-Forwarded-For value that cannot be overridden by a client-supplied header.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.