Hydro: Insufficient session expiration when recreating sessions
Key facts
- Attack vector
- Network
- Privileges required
- High
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-613.
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 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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| hydro-dev | Hydro | 4.10.4 to before 5.0.2 | 5.0.2 | Patch available | CNA |
| — | hydrooj (npm) | 4.10.4 to before 5.0.2 | 5.0.2 | Patch available | GHSA-94jp-7776-qj6q |
- Hydro Vendorhydro-dev Affected 4.10.4 to before 5.0.2 Fixed in 5.0.2 Patch available CNA
- hydrooj (npm) Vendor— Affected 4.10.4 to before 5.0.2 Fixed in 5.0.2 Patch available GHSA-94jp-7776-qj6q
Remediation
- Fix · CNA Hydro (hydro-dev) Fixed in 5.0.2
- Fix · GHSA-94jp-7776-qj6q hydrooj (npm) Fixed in 5.0.2 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-55617
- 2026-10-03 Alias added: GHSA-94jp-7776-qj6q
References
Other 5
- https://github.com/hydro-dev/Hydro/security/advisories/GHSA-94jp-7776-qj6q
- https://github.com/hydro-dev/Hydro/pull/1173
- https://github.com/hydro-dev/Hydro/commit/8450390fcce5f7dc3f11c43a14f1d76dbb949a0d
- https://github.com/hydro-dev/Hydro/commit/8d76be8f0b83d911bf7671962b0467e9d4b5719a
- https://github.com/hydro-dev/Hydro
Sources
- CVE-2026-55617 · CVE Program
- CVE-2026-55617 · NVD
- FIRST EPSS
- GHSA-94jp-7776-qj6q · GitHub Advisory Database · CC BY 4.0
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