{"id":"CVE-2026-78551","summary":"RansomLook Login Endpoint Allows Timing-Based Username Enumeration and Unthrottled Authentication Attempts","details":"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.\n\nFor 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.\n\nIn 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.\n\nThe 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.","modified":"2026-08-28T11:30:26.216124985Z","published":"2026-08-24T19:20:03.145Z","database_specific":{"cwe_ids":["CWE-307","CWE-400"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78551.json","cna_assigner":"CIRCL"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78551.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-78551"},{"type":"FIX","url":"https://github.com/RansomLook/RansomLook/commit/8602740347b0e928ad9fbaf5bc6ff242337dec6b"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ransomlook/ransomlook","events":[{"introduced":"0"},{"fixed":"8602740347b0e928ad9fbaf5bc6ff242337dec6b"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"last_affected":"2.0.0"}],"source":["AFFECTED_FIELD","REFERENCES"]}}],"versions":["2.0.0","1.9.0","1.8.0","1.6.0","1.5.0","1.4.0","1.3.0","1.2.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-78551.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N"}]}