{"id":"CVE-2026-48109","aliases":["GHSA-hv8m-jj95-wg3x"],"title":" MessagePack's LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input","summary":" MessagePack's LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input","severity":"high","cvss":8.2,"cwe":["CWE-20"],"vendor":"MessagePack","product":"MessagePack","ecosystem":"nuget","affected":["MessagePack < 2.5.301","MessagePack >= 3.0.214-rc.1, < 3.1.7"],"patched":["MessagePack 2.5.301","MessagePack 3.1.7"],"published":"2026-06-11","updated":"2026-06-25","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-hv8m-jj95-wg3x","references":[{"url":"https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-hv8m-jj95-wg3x"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-48109"},{"url":"https://github.com/advisories/GHSA-hv8m-jj95-wg3x"}],"tags":["ghsa","nuget"],"epss":0.00509,"epssPercentile":0.40847,"ingestedAt":"2026-07-07T15:41:59.277Z","slug":"CVE-2026-48109","body":"## Overview\n\n### Impact\n\nA vulnerability exists in the optional LZ4 decompression path used by MessagePack compression modes `Lz4Block` and `Lz4BlockArray`.\n\nThe 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.\n\nThis issue affects applications that deserialize untrusted data while LZ4 compression is enabled.\n\n### Patches\n\nThe v2 versions are patched as of 2.5.301.\nThe v3 versions are patched as of 3.1.7.\n\n### Workarounds\n\nInstead of upgrading, an application may take the following precautions:\n\n1. Disable LZ4 compression for untrusted input paths (`Lz4Block`, `Lz4BlockArray`).\n2. Only accept compressed payloads from strongly trusted producers.\n3. Isolate deserialization in a separate process/container with restart supervision to limit availability impact.\n\n### Resources\n\n- MESSAGEPACKCSHARP-010\n\n## Affected packages\n\n- `MessagePack < 2.5.301`\n- `MessagePack >= 3.0.214-rc.1, < 3.1.7`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `MessagePack 2.5.301`\n- `MessagePack 3.1.7`","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":45.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}