msgpack-java — security advisory
MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getData() is invoked, the library attempts to allocate a byte array of the declared length without enforcing any upper bound. A malicious .msgpack file of only a few bytes can therefore trigger unbounded heap allocation, resulting in JVM heap exhaustion, process termination, or service unavailability. This vulnerability is triggered during model loading / deserialization, making it a model format vulnerability suitable for remote exploitation. The vulnerability enables a remote denial-of-service attack against applications that deserialize untrusted .msgpack model files using MessagePack for Java. A specially crafted but syntactically valid .msgpack file containing an EXT32 object with an attacker-controlled, excessively large payload length can trigger unbounded memory allocation during deserialization. When the model file is loaded, the library trusts the declared length metadata and attempts to allocate a byte array of that size, leading to rapid heap exhaustion, excessive garbage collection, or immediate JVM termination with an OutOfMemoryError. The attack requires no malformed bytes,
- Products
- msgpack-java
- Affected versions
- 0.8.18-2, 0.8.19-1, 0.8.22-2, 0.9.0-1, 0.9.0-2, 0.9.5-1, 0.9.6-1, 0.9.6-1build1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-21452
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:56 UTC · Revision 1
Source evidence
MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getData() is invoked, the library attempts to allocate a byte array of the declared length without enforcing any upper bound. A malicious .msgpack file of only a few bytes can therefore trigger unbounded heap allocation, resulting in JVM heap exhaustion, process termination, or service unavailability. This vulnerability is triggered during model loading / deserialization, making it a model format vulnerability suitable for remote exploitation. The vulnerability enables a remote denial-of-service attack against applications that deserialize untrusted .msgpack model files using MessagePack for Java. A specially crafted but syntactically valid .msgpack file containing an EXT32 object with an attacker-controlled, excessively large payload length can trigger unbounded memory allocation during deserialization. When the model file is loaded, the library trusts the declared length metadata and attempts to allocate a byte array of that size, leading to rapid heap exhaustion, excessive garbage collection, or immediate JVM termination with an OutOfMemoryError. The attack requires no malformed bytes,
osv:UBUNTU-CVE-2026-21452
msgpack-java
Fixed versions: Not specified
msgpack-java
Fixed versions: Not specified
msgpack-java
Fixed versions: Not specified
msgpack-java
Fixed versions: Not specified
msgpack-java
Fixed versions: Not specified
msgpack-java
Fixed versions: Not specified
Complete source record
{
"id": "ac2471786d290f597083e50f2daf28c1a7b7ccfda537d305d8e2203172a4ea92",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-21452",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-21452",
"summary": "MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getData() is invoked, the library attempts to allocate a byte array of the declared length without enforcing any upper bound. A malicious .msgpack file of only a few bytes can therefore trigger unbounded heap allocation, resulting in JVM heap exhaustion, process termination, or service unavailability. This vulnerability is triggered during model loading / deserialization, making it a model format vulnerability suitable for remote exploitation. The vulnerability enables a remote denial-of-service attack against applications that deserialize untrusted .msgpack model files using MessagePack for Java. A specially crafted but syntactically valid .msgpack file containing an EXT32 object with an attacker-controlled, excessively large payload length can trigger unbounded memory allocation during deserialization. When the model file is loaded, the library trusts the declared length metadata and attempts to allocate a byte array of that size, leading to rapid heap exhaustion, excessive garbage collection, or immediate JVM termination with an OutOfMemoryError. The attack requires no malformed bytes,",
"evidence": "osv:UBUNTU-CVE-2026-21452",
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"modified": "2026-10-17T12:59:54.734767960Z",
"provider": "osv",
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"references": [
"https://ubuntu.com/security/CVE-2026-21452",
"https://www.cve.org/CVERecord?id=CVE-2026-21452",
"https://github.com/msgpack/msgpack-java/security/advisories/GHSA-cw39-r4h6-8j3x",
"https://github.com/msgpack/msgpack-java/commit/daa2ea6b2f11f500e22c70a22f689f7a9debdeae",
"https://github.com/msgpack/msgpack-java/releases/tag/v0.9.11"
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},
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"evidence": "/upstream"
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"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 359939,
"published_at": "2026-01-02T21:16:00+00:00"
}