How severe is GHSA-cmp6-m4wj-q63q?

No CVSS score has been assigned to GHSA-cmp6-m4wj-q63q yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-cmp6-m4wj-q63q?

GHSA-cmp6-m4wj-q63q affects the following packages: at.yawk.lz4:lz4-java (Maven), org.lz4:lz4-java (Maven), org.lz4:lz4-pure-java (Maven), net.jpountz.lz4:lz4 (Maven). Ecosystems affected: Maven.

How do I fix GHSA-cmp6-m4wj-q63q?

Update at.yawk.lz4:lz4-java to 1.10.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-cmp6-m4wj-q63q is resolved across your whole dependency graph.

How do I detect GHSA-cmp6-m4wj-q63q in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for at.yawk.lz4:lz4-java. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate GHSA-cmp6-m4wj-q63q if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against GHSA-cmp6-m4wj-q63q?

O3 pinpoints whether GHSA-cmp6-m4wj-q63q is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is GHSA-cmp6-m4wj-q63q actively exploited in the wild?

No public exploit code has been indexed for GHSA-cmp6-m4wj-q63q 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 GHSA-cmp6-m4wj-q63q?

GHSA-cmp6-m4wj-q63q has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th 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.

When was GHSA-cmp6-m4wj-q63q published, and has it been updated?

GHSA-cmp6-m4wj-q63q was published on December 5, 2025 and was last updated on March 6, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

GHSA-cmp6-m4wj-q63q

yawkat LZ4 Java has a possible information leak in Java safe decompressor

Also known asCVE-2025-66566

Published

Dec 5, 2025

Updated

Mar 6, 2026

Affected

4 pkgs

Patched

1 / 4

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk41th percentile+0.47%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

4 pkgs affected

☕at.yawk.lz4:lz4-java☕org.lz4:lz4-java☕org.lz4:lz4-pure-java☕net.jpountz.lz4:lz4

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

Summary

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.

Details

During the decompression process, the lz4 algorithm may have to repeat data that was previously decompressed in the same input frame. In the Java implementation, this is implemented by copy operations within the output buffer.

With a crafted input, an attacker may induce the Java implementation to copy from a region in the output buffer that does not contain decompressed data yet. If that region contains sensitive information because the output buffer was not cleared prior to decompression, that data will then be copied to the decompressed output.

LZ4Factory.nativeInstance().safeDecompressor() is not affected.
LZ4Factory.nativeInstance().fastDecompressor() is affected because it actually uses safeInstance() since 1.8.1. In 1.8.0 and earlier versions, this implementation is instead vulnerable to the more severe CVE‐2025‐12183, so downgrading is not a solution.
Both decompressors of LZ4Factory.safeInstance(), LZ4Factory.unsafeInstance() and LZ4Factory.fastestJavaInstance() are affected.
LZ4Factory.fastestInstance() uses the nativeInstance or fastestJavaInstance depending on platform. LZ4Factory.fastestInstance().fastDecompressor() is always affected, while LZ4Factory.fastestInstance().safeDecompressor() is affected only when JNI cannot be used (e.g. on unsupported platforms).

Independent of this vulnerability, it is recommended that users migrate from fastDecompressor to safeDecompressor, as the latter is more performant (despite the name).

The impact of this vulnerability depends on how user code interacts with the decompression API. Users that allocate a new destination buffer each time, or use only zeroed buffers, are not impacted. When the buffer is reused, however, the confidentiality impact can be severe. This vulnerability is marked as VC:H out of caution.

Mitigation

lz4-java 1.10.1 fixes this issue without requiring changes in user code.

If you cannot upgrade to 1.10.1, you can mitigate this vulnerability by zeroing the output buffer before passing it to the decompression function.

Relation to CVE‐2025‐12183

This CVE is a different attack than CVE‐2025‐12183, affecting different implementations with different impact. This new vulnerability was discovered by CodeIntelligence during research that followed up on CVE‐2025‐12183. Users are recommended to upgrade to 1.10.1 to fix both vulnerabilities.

Affected Packages

4 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`at.yawk.lz4:lz4-java`	all versions	1.10.1
☕Maven	`org.lz4:lz4-java`	all versions	No fix
☕Maven	`org.lz4:lz4-pure-java`	all versions	No fix
☕Maven	`net.jpountz.lz4:lz4`	all versions	No fix

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for at.yawk.lz4:lz4-java. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update at.yawk.lz4:lz4-java to 1.10.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-cmp6-m4wj-q63q is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-cmp6-m4wj-q63q is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-cmp6-m4wj-q63q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### Summary 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. ### Details During the decompression process, the lz4 algorithm may have to repeat data that was previously decompressed in the same input frame. In the Java implementation, this is implemented by copy operations w

O3 Security · Impact-Aware SCA

Is GHSA-cmp6-m4wj-q63q in your dependencies?

O3 detects GHSA-cmp6-m4wj-q63q across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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