CVE-2026-55617

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.

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Weakness Type (CWE)

CWE-613 CWE-613

References

Other References

https://github.com/hydro-dev/Hydro/commit/8450390fcce5f7dc3f11c43a14f1d76dbb949a0d https://github.com/hydro-dev/Hydro/commit/8d76be8f0b83d911bf7671962b0467e9d4b5719a https://github.com/hydro-dev/Hydro/pull/1173 https://github.com/hydro-dev/Hydro/security/advisories/GHSA-94jp-7776-qj6q

Frequently Asked Questions

What is CVE-2026-55617? +

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.

How do I check if I'm vulnerable to CVE-2026-55617? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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