---
id: CVE-2026-55617
title: Hydro is a next-generation high-performance online judge platform
summary: >-
  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 tok…
severity: medium
cvss: 6.9
cvssVector: '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'
cwe:
  - CWE-613
vendor: hydro-dev
product: Hydro
affected:
  - 'Hydro >= 4.10.4, < 5.0.2'
patched:
  - hydrooj 5.0.2
published: '2026-09-15'
updated: '2026-09-15'
sourceUpdated: '2026-09-15T19:17:22.433'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55617'
references:
  - url: >-
      https://github.com/hydro-dev/Hydro/commit/8450390fcce5f7dc3f11c43a14f1d76dbb949a0d
    label: security-advisories@github.com
  - url: >-
      https://github.com/hydro-dev/Hydro/commit/8d76be8f0b83d911bf7671962b0467e9d4b5719a
    label: security-advisories@github.com
  - url: 'https://github.com/hydro-dev/Hydro/pull/1173'
    label: security-advisories@github.com
  - url: 'https://github.com/hydro-dev/Hydro/security/advisories/GHSA-94jp-7776-qj6q'
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-94jp-7776-qj6q'
tags:
  - nvd
  - cve.org
  - ghsa
  - npm
ecosystem: npm
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-15T17:38:23.906162Z'
cvssSource: cna
ingestedAt: '2026-06-29T14:31:47.002Z'
epss: 0.00473
epssPercentile: 0.38328
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-55617)

Affected packages:

- `hydrooj >= 4.10.4, <= 5.0.1`

Patched in:

- `hydrooj 5.0.2`

Source: https://github.com/advisories/GHSA-94jp-7776-qj6q