{"answers":{"affected":"2 open source packages ship an affected version, including org.msgpack:msgpack-core. It affects 1 product.","exploited":"It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21452 exists.","fix":"Upgrade org.msgpack:msgpack-core to 0.9.11 or later.","what":"CVE-2026-21452 is a high-severity denial of service vulnerability in msgpack-java, published on 2 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-21452 and fix it if it is affected.\n\nWhat it is: CVE-2026-21452 is a high-severity denial of service vulnerability in msgpack-java, published on 2 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21452 exists.\n\nAffected packages and fixed versions:\n- org.msgpack:msgpack-core (Maven): affected all versions; fixed in 0.9.11\n- org.msgpack:msgpack-core (Maven): affected all versions; fixed in 0.9.11\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-21452/ (Markdown: https://insights.sbomify.com/CVE-2026-21452/index.md)","id":"CVE-2026-21452","markdown":"https://insights.sbomify.com/CVE-2026-21452/index.md","name":"CVE-2026-21452","record":{"aliases":["CLEANSTART-2026-ED59299","CLEANSTART-2026-MQ41699","DEBIAN-CVE-2026-21452","GHSA-cw39-r4h6-8j3x","UBUNTU-CVE-2026-21452"],"analysis":{"component_type":"library","fix_type":"upgrade","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Java serialization library","requires_auth":"none","summary":"Remote attackers can cause denial of service in Java applications by submitting malicious MessagePack files that trigger unbounded memory allocation.","user_interaction":"not_required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"GitHub_M","cpe":[{"product":"messagepack","vendor":"msgpack"}],"cvss":{"score":7.5,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"cwes":[{"id":"CWE-789","name":"Memory Allocation with Excessive Size Value"},{"id":"CWE-400","name":"Uncontrolled Resource Consumption"}],"description":"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, user interaction, or elevated privileges and can be exploited remotely in real-world environments such as model registries, inference services, CI/CD pipelines, and cloud-based model hosting platforms that accept or fetch .msgpack artifacts. Because the malicious file is extremely small yet valid, it can bypass basic validation and scanning mechanisms, resulting in complete service unavailability and potential cascading failures in production systems. Version 0.9.11 fixes the vulnerability.","ecosystems":["Maven"],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"weaponised"},"has_fix":true,"headline":"MessagePack for Java Vulnerable to Remote DoS via Malicious EXT Payload Allocation","id":"CVE-2026-21452","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"Maven","product":null,"products":[],"type":"denial_of_service","year":"2026"},"n_packages":2,"n_references":3,"next":{"headline":"listmonk Vulnerable to Stored XSS Leading to Admin Account Takeover","id":"CVE-2026-21483"},"packages":[{"ecosystem":"Maven","fixed":["0.9.11"],"introduced":["0"],"last_affected":[],"package":"org.msgpack:msgpack-core","purl":null,"source":"GHSA-cw39-r4h6-8j3x"},{"ecosystem":"Maven","fixed":["0.9.11"],"introduced":["0"],"last_affected":[],"package":"org.msgpack:msgpack-core","purl":"pkg:maven/org.msgpack/msgpack-core","source":"GHSA-cw39-r4h6-8j3x"}],"prev":{"headline":"Bagisto has HTML Filter Bypass that Enables Stored XSS","id":"CVE-2026-21451"},"products":["msgpack-java"],"published":"2026-01-02","related":[{"cvss_score":7.5,"headline":"MessagePack: Out-of-bounds read/crash on Unpacker reuse after caught error","id":"CVE-2026-57585","kev_date_added":null,"published":"2026-06-30"},{"cvss_score":2.1,"headline":"MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure","id":"CVE-2026-54522","kev_date_added":null,"published":"2026-07-30"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CC BY 4.0","name":"GitHub Advisory Database","prefix":"GHSA"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"yes","exploitation":"poc","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-01-02","vendors":["msgpack"]},"summary":"Remote attackers can cause denial of service in Java applications by submitting malicious MessagePack files that trigger unbounded memory allocation.","url":"https://insights.sbomify.com/CVE-2026-21452/"}