Summary
yawkat LZ4 Java: LZ4FrameInputStream reallocates block buffers for every frame, allowing CPU and GC amplification from small inputs
LZ4FrameInputStream allocates two new buffers of the frame's maximum block size, up to 4 MiB each, every time it reads a frame header. Because concatenated frames are read by default, an input made of many minimal empty frames forces about 8 MiB of zeroed heap allocation for every 11 input bytes.
Details
In net.jpountz.lz4.LZ4FrameInputStream.readHeader():
maxBlockSize = frameInfo.getBD().getBlockMaximumSize();
compressedBuffer = new byte[maxBlockSize]; // Reused during different compressions
rawBuffer = new byte[maxBlockSize];
buffer = ByteBuffer.wrap(rawBuffer);
This runs for every frame, and the previous frame's arrays are never reused. A valid 11-byte frame consists of the magic number, FLG 0x60, BD 0x70 (4 MiB blocks), the header checksum, and an immediate end mark. It carries no data, yet triggers the full 8 MiB allocation. new LZ4FrameInputStream(in) reads concatenated frames by default.
In local measurements on JDK 25, 10,000 such frames (110 KB of input) took about 8 seconds of CPU to read, roughly 70 seconds per MiB of input. This was similar under G1, Parallel, Serial and ZGC. A legitimate stream costs orders of magnitude less per input byte.
Impact
Applications that decode attacker-controlled LZ4 frame data with LZ4FrameInputStream can be made to spend large amounts of CPU and GC time relative to the input size. Live heap stays bounded at about 8 MiB and the stream produces no output, so decompressed-size limits do not help. Cost grows linearly with input size, so the practical limit is the compressed input size the application accepts. Availability impact only.
Applications using readSingleFrame = true perform only one allocation and are not affected.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
CVE-2026-106450 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.11.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in lz4-java 1.11.4. LZ4FrameInputStream now allocates its block buffers only when a block needs them and reuses them across frames, never shrinking them. The content checksum hash and the skippable-frame skip buffer are also reused instead of being created for every frame. Decompression is limited to the current frame's maximum block size.
For older versions, the workaround is to limit the compressed input size accepted from untrusted sources, or use single-frame mode where that is sufficient.
Frequently Asked Questions
- What is CVE-2026-106450? CVE-2026-106450 is a medium-severity allocation of resources without limits or throttling vulnerability in at.yawk.lz4:lz4-java (maven), affecting versions <= 1.11.3. It is fixed in 1.11.4. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- How severe is CVE-2026-106450? CVE-2026-106450 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-106450?
at.yawk.lz4:lz4-java(maven) (versions <= 1.11.3)org.lz4:lz4-java(maven) (versions <= 1.8.1)
- Is there a fix for CVE-2026-106450? Yes. CVE-2026-106450 is fixed in 1.11.4. Upgrade to this version or later.
- Is CVE-2026-106450 exploitable, and should I be worried? Whether CVE-2026-106450 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-106450 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-106450? Upgrade
at.yawk.lz4:lz4-javato 1.11.4 or later.