Security Digest · Vulnerability record
CVE-2025-6544: H2O affected by a deserialization vulnerability
A deserialization vulnerability exists in h2oai/h2o-3 versions
CVSS 9.8 Critical EPSS 0.9% · p60
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.9%, percentile 60: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 60% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
ai.h2o:h2o-core(Maven) <= 3.46.0.7, no fixed version listed;h2o(PyPI) <= 3.46.0.7, no fixed version listed. Check your lockfile, including transitive dependencies.
What it is
A deserialization vulnerability exists in h2oai/h2o-3 versions
From the GitHub advisory
A deserialization vulnerability exists in h2oai/h2o-3 versions
Weakness type: CWE-502.
Product: ai.h2o:h2o-core (Maven) · Assigned by: @huntr_ai · Published: 2025-09-21
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Maven | ai.h2o:h2o-core | <= 3.46.0.7 | none listed |
| PyPI | h2o | <= 3.46.0.7 | none listed |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| h2oai | h2oai/h2o-3 | unspecified < 3.46.8 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| @huntr_ai | 3.0 | 9.8 Critical | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| GitHub | 3.1 | 9.8 | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.92% probability of exploitation activity in the next 30 days; percentile 60.
Timeline
- — CVE record published by @huntr_ai
- — CVE record last updated
- — GitHub-reviewed advisory GHSA-5w3j-gwgh-4rfv published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-5w3j-gwgh-4rfv github.com
- CVE.org record CVE-2025-6544 cve.org
- NVD entry CVE-2025-6544 nvd.nist.gov
Other references from the CVE record and advisory
- huntr.com huntr.com
- github.com github.com