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Fencer Vulns
high 7.5

CVE-2026-48502 json

MessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflows

published 2026-06-22 4 mo ago modified 2026-06-25 4 mo ago also GHSA-382j-8mxh-c7x2 , EUVD-2026-38389

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 38%
public exploits
0
none known

Summary

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePackReader.ReadDateTime() can allocate stack memory based on an attacker-controlled MessagePack extension length. In the slow path for timestamp extension parsing, the computed tokenSize includes the extension body length from the wire and is used in a stackalloc operation before the extension length is validated as one of the valid timestamp sizes. A very small payload can claim a large timestamp extension body and cause a stack allocation large enough to trigger an uncatchable StackOverflowException, terminating the host process. This vulnerability is fixed in 2.5.301 and 3.1.7.

Patch / fix

  • nuget MessagePack 3.1.7
  • messagepack messagepack 2.5.301, 3.1.7

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.44% chance of exploitation in the next 30 days, higher than 38% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CNA 4.0 8.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
nuget MessagePack
>=3.0, <3.1.7
3.1.7

Affected products

  • MessagePack-CSharp MessagePack-CSharp

Classification

Weakness
  • CWE-125 Out-of-bounds Read
  • CWE-190 Integer Overflow or Wraparound
  • CWE-407 Inefficient Algorithmic Complexity
  • CWE-409 Improper Handling of Highly Compressed Data (Data Amplification)
  • CWE-470 Use of Externally-Controlled Input to Select Classes or Code
  • CWE-502 Deserialization of Untrusted Data
  • CWE-674 Uncontrolled Recursion
  • CWE-789 Memory Allocation with Excessive Size Value
  • CWE-1188 Initialization of a Resource with an Insecure Default

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.