How severe is CVE-2025-66566?

CVE-2025-66566 has a CVSS 4.0 base score of 8.2, rated high severity.

Is CVE-2025-66566 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2025-66566?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2025-66566 have an EU (EUVD) identifier?

Yes. CVE-2025-66566 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201456.

When was CVE-2025-66566 published?

CVE-2025-66566 was published on 2025-12-05 and last updated on 2026-06-17.

CVE-2025-66566

CVE-2025-66566 is a high-severity vulnerability with a CVSS 4.0 base score of 8.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-201.

Key facts

Severity: High (CVSS 4.0 base score 8.2)
EPSS exploit prediction: 1% (43rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-201456
Weakness: CWE-201
Published: 2025-12-05
Last modified: 2026-06-17

Description

yawkat LZ4 Java provides LZ4 compression for Java. Insufficient clearing of the output buffer in Java-based decompressor implementations in lz4-java 1.10.0 and earlier allows remote attackers to read previous buffer contents via crafted compressed input. In applications where the output buffer is reused without being cleared, this may lead to disclosure of sensitive data. JNI-based implementations are not affected. This vulnerability is fixed in 1.10.1.

Frequently asked questions

What is CVE-2025-66566?: yawkat LZ4 Java provides LZ4 compression for Java. Insufficient clearing of the output buffer in Java-based decompressor implementations in lz4-java 1.10.0 and earlier allows remote attackers to read previous buffer contents via crafted compressed input. In applications where the output buffer is reused without being cleared, this may lead to disclosure of sensitive data. JNI-based implementations are not affected. This vulnerability is fixed in 1.10.1.
How severe is CVE-2025-66566?: CVE-2025-66566 has a CVSS 4.0 base score of 8.2, rated high severity.
Is CVE-2025-66566 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2025-66566?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-66566 have an EU (EUVD) identifier?: Yes. CVE-2025-66566 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201456.
When was CVE-2025-66566 published?: CVE-2025-66566 was published on 2025-12-05 and last updated on 2026-06-17.

References

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