CVE-2026-55617

CVE-2026-55617 · Hydro: Insufficient session expiration when recreating sessions

This page contains facts from public vulnerability sources. Check the original advisory before updating.

Hydro is a next-generation high-performance online judge platform. From 4.10.4 until 5.0.2, the session recreation logic in packages/hydrooj/src/service/layers/base.ts creates a replacement session token without deleting the previous token from the server-side session token store, so an old sid cookie can remain valid after logout or another renewal flow. An attacker who possesses a victim's previously valid stale cookie can replay it over HTTP or HTTPS without knowing the victim's username or password and without victim interaction at exploitation time. Successful replay can take over the victim's account, disclose private data, and permit unauthorized modification or deletion of data available to that account. This issue is fixed in version 5.0.2.

CVSS 6.9 · Medium · EPSS 0.5% · Fix available

Published

2026-09-15T14:45:11.664Z

Updated

2026-09-15T18:02:57.088Z

Stack: node

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