How severe is CVE-2026-55617?

No CVSS score has been assigned to CVE-2026-55617 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-55617?

CVE-2026-55617 affects the following packages: hydrooj (npm). Ecosystems affected: npm.

How do I fix CVE-2026-55617?

Update hydrooj to 5.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55617 is resolved across your whole dependency graph.

How do I detect CVE-2026-55617 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hydrooj, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-55617 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-55617 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55617 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-55617?

CVE-2026-55617 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 39th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-55617?

CVE-2026-55617 is classified as CWE-613 (CWE-613). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-55617 published, and has it been updated?

CVE-2026-55617 was published on September 15, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-55617 — hydrooj

Fix: hydro-dev/Hydro@8450390

CVE-2026-55617 is a CWE-613 vulnerability in hydrooj. A fix is available for hydrooj — see the affected versions and patch details below.

Hydro: Insufficient session expiration when recreating sessions

Also known asGHSA-94jp-7776-qj6q

Published

Sep 15, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55617.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs39th percentile — riskier than 39% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

5other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

hydroojnpm

2Kdownloads / week

Description

Impact

Hydro contains an insufficient session expiration vulnerability in its session recreation logic. When a session is recreated, including during logout or other session renewal flows, Hydro creates a new session token but does not delete the previous server-side session token.

As a result, an old sid cookie may remain valid even after the legitimate user logs out or the session is recreated. An attacker who has obtained a victim's previous sid cookie can replay that cookie over HTTP or HTTPS and continue to access the affected Hydro instance as the victim.

The attacker does not need the victim's username or password. Exploitation requires possession of a previously valid stale sid cookie, but no user interaction is required at exploitation time.

Successful exploitation may allow account takeover within the affected Hydro instance. For a normal user account, this may allow disclosure of private data and unauthorized modification or deletion of data available to the victim.

Patches

The issue has been patched by deleting the old server-side session token before creating a new one during session recreation.

Patched in:

Pull request: https://github.com/hydro-dev/Hydro/pull/1173
Patch commit: https://github.com/hydro-dev/Hydro/commit/8450390fcce5f7dc3f11c43a14f1d76dbb949a0d
Merge commit: https://github.com/hydro-dev/Hydro/commit/8d76be8f0b83d911bf7671962b0467e9d4b5719a

Users should upgrade to a version containing this patch.

Workarounds

If upgrading immediately is not possible, administrators should reduce the risk by forcing all existing sessions to expire or by clearing the server-side session token store after applying a local patch.

Administrators should also review logs for suspicious use of stale sid cookies and rotate any exposed session cookies. However, these mitigations do not fully fix the vulnerability. The recommended remediation is to upgrade to a patched version.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`hydrooj`	≥ 4.10.4&&< 5.0.2	5.0.2`npm install hydrooj@5.0.2`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hydrooj, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hydrooj to 5.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55617 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Impact Hydro contains an insufficient session expiration vulnerability in its session recreation logic. When a session is recreated, including during logout or other session renewal flows, Hydro creates a new session token but does not delete the previous server-side session token. As a result, an old sid cookie may remain valid even after the legitimate user logs out or the session is recreated. An attacker who has obtained a victim's previous sid cookie can replay that cookie over HTTP or HTTPS and continue to access the affected Hydro instance as the victim. The attacker does not nee

O3 Security · Impact-Aware SCA

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