CVE-2026-55617
MEDIUMDescription
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 to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v4 Vector
Exploitability
Impact
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Exploit Intelligence
Low risk: more likely to be exploited than 20% of all known CVEs.
References
Related Vulnerabilities
Other CWE-613 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-2595 | Critical | 9.8 | 17% | - | - |
| CVE-2023-30403 | High | 7.5 | 14% | - | - |
| CVE-2020-27422 | Critical | 9.8 | 7.9% | - | - |
| CVE-2014-3616 | Medium | 4.3 | 5.7% | - | Fix |
| CVE-2021-3144 | Critical | 9.1 | 5.2% | - | Fix |
| CVE-2021-24019 | High | 8.1 | 3.9% | - | Fix |
Common questions
How do I fix CVE-2026-55617?
No published fix for CVE-2026-55617 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-55617 being actively exploited?
Not that we know of. CVE-2026-55617 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.27% is the estimated probability that it will be exploited in the next 30 days. That is higher than 20% of all scored CVEs.
How severe is CVE-2026-55617?
CVE-2026-55617 has a CVSS v4 base score of 6.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-15.