Hydro: Insufficient session expiration when recreating sessions

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.

Source published

15 Sep 2026 14:45:11 UTC

Source modified

15 Sep 2026 18:02:57 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N