CVE-2026-48109 json
MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input
published 2026-06-11 4 mo ago modified 2026-09-10 1 mo ago also GHSA-hv8m-jj95-wg3x , EUVD-2026-38390
- cvss
- 8.2
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 43%
- public exploits
- 0
- none known
Summary
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, 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 vulnerability is fixed in 2.5.301 and 3.1.7.
Patch / fix
- nuget MessagePack 2.5.301, 3.1.7
- messagepack messagepack 2.5.301, 3.1.7
CISA SSVC
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 4 mo ago
Exploit prediction
0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 8.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H |
| GitHub | 3.1 | 8.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| nuget | MessagePack | <2.5.301 >=3.0.214-rc.1, <3.1.7 |
2.5.301 3.1.7 |
Affected products
- MessagePack-CSharp MessagePack-CSharp
Classification
- Weakness
-
- CWE-20 Improper Input Validation
References
-
github.com
/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-hv8m-jj95-wg3x
web, mitigation, vendor-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-48109
advisory
-
github.com
/MessagePack-CSharp/MessagePack-CSharp
package
Sources
- CVE List CVE-2026-48109
- GitHub Advisory GHSA-hv8m-jj95-wg3x
- NVD CVE-2026-48109
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