CVE-2026-55617 Hydro: Insufficient session expiration when recreating sessions
Attackers can replay stale session cookies to take over accounts and access or modify data due to insufficient session expiration in Hydro.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55617?
CVE-2026-55617 is a medium-severity authentication bypass vulnerability in hydro-dev Hydro, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
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.
Weakness: CWE-613
Which versions are affected by CVE-2026-55617?
2 open source packages ship an affected version, including hydrooj.
| Package | Affected | Fixed in |
|---|---|---|
hydrooj npm | From 4.10.4 | 5.0.2 |
hydrooj npm | From 4.10.4 | 5.0.2 |
How do I fix CVE-2026-55617?
Upgrade hydrooj to 5.0.2 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-55617 being exploited?
There is no known exploitation of CVE-2026-55617 in the wild and no public exploit code.
Sources
Also known as GHSA-94jp-7776-qj6q.