CVE-2026-48109 is a high-severity security vulnerability in MessagePack (nuget), affecting versions < 2.5.301. It is fixed in 2.5.301, 3.1.7.
Impact A vulnerability exists in the optional LZ4 decompression path used by MessagePack compression modes Lz4Block and Lz4BlockArray. The decoder implementation is based on a deprecated fast-decompression algorithm that does not take a source-length bound. A remote attacker can send a crafted MessagePack payload with manipulated LZ4 token/length fields to force out-of-bounds reads from the compressed input buffer. In affected environments, this can trigger an AccessViolationException during decompression, causing process termination (denial of service). Under some conditions, limited unintended memory disclosure from over-read data may also be possible before failure. This issue affects applications that deserialize untrusted data while LZ4 compression is enabled. Patches The v2 versions are patched as of 2.5.301. The v3 versions are patched as of 3.1.7. Workarounds Instead of upgrading, an application may take the following precautions: Disable LZ4 compression for untrusted input paths (Lz4Block, Lz4BlockArray). Only accept compressed payloads from strongly trusted producers. Isolate deserialization in a separate process/container with restart supervision to limit availability impact. Resources MESSAGEPACKCSHARP-010
CVE-2026-48109 has a CVSS score of 8.2 (High). 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 (2.5.301, 3.1.7). Upgrading removes the vulnerable code path.
nuget
MessagePack (< 2.5.301)MessagePack (>= 3.0.214-rc.1, < 3.1.7)MessagePack → 2.5.301 (nuget)MessagePack → 3.1.7 (nuget)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.
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Upgrade the following packages to resolve this vulnerability:
MessagePack to 2.5.301 or laterMessagePack to 3.1.7 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-48109 is a high-severity security vulnerability in MessagePack (nuget), affecting versions < 2.5.301. It is fixed in 2.5.301, 3.1.7.
CVE-2026-48109 has a CVSS score of 8.2 (High). 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.
MessagePack (nuget) versions < 2.5.301 is affected.
Yes. CVE-2026-48109 is fixed in 2.5.301, 3.1.7. Upgrade to this version or later.
Whether CVE-2026-48109 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
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.
MessagePack to 2.5.301 or laterMessagePack to 3.1.7 or later