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Vulnerability · Published Sep 15, 2026 · Assigned by GitHub_M

CVE-2026-55617Hydro: Insufficient session expiration when recreating sessions

Medium 6.9

In plain English

A medium-severity security flaw in Hydro from hydro-dev. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.9Medium
Exploit odds (30 days)0.5%top 58.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npmhydrooj5.0.2GHSA-94jp-7776-qj6q

Affected products (as reported)

VendorProductVersions
hydro-dev Hydro >= 4.10.4, < 5.0.2

Weakness: CWE-613 · Vector: 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

References