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TI-2026-69600 Aliases CVE-2026-107299GHSA-26wq-p25c-j6fv

Reserved byte in msgpack5 causes unbounded stream buffering

Priority LOW 27CWE-228Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
—
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.

Summary

msgpack5 before 6.1.0, a MessagePack v5 implementation for node.js and the browser, mishandles invalid input (CWE-228). Its streaming decoder treats the reserved byte 0xc1 as incomplete input instead of invalid input. Subsequent data stays buffered while the decoder waits for bytes that can never make the value valid. A remote peer without privileges can exhaust memory.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder treats the reserved MessagePack byte 0xc1 as incomplete input instead of invalid input. When 0xc1 begins a stream, subsequent data remains buffered while the decoder waits for bytes that cannot make the value valid, allowing a remote peer to exhaust memory. This issue is fixed in version 6.1.0.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00389 33rd percentileScored 2026-11-07
Fix Fixed msgpack5 (mcollina): 6.1.0msgpack5 (npm): 6.1.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
mcollinamsgpack5before 6.1.06.1.0Patch availableCNA
—msgpack5 (npm)before 6.1.06.1.0Patch availableGHSA-26wq-p25c-j6fv
  • msgpack5 Vendormcollina Affected before 6.1.0 Fixed in 6.1.0 Patch available CNA
  • msgpack5 (npm) Vendor— Affected before 6.1.0 Fixed in 6.1.0 Patch available GHSA-26wq-p25c-j6fv

Remediation

Upgrade the msgpack5 npm package to version 6.1.0, which fixes this issue.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

  • Fix · CNA msgpack5 (mcollina) Fixed in 6.1.0
  • Fix · GHSA-26wq-p25c-j6fv msgpack5 (npm) Fixed in 6.1.0 Advisory →

Timeline

  1. 2026-10-08 Threatist record created from CVE-2026-107299
  2. 2026-10-08 Alias added: GHSA-26wq-p25c-j6fv
  3. 2026-10-10 CISA SSVC decision points changed
  4. 2026-10-10 Priority changed: MEDIUM → LOW

References

Other 4

  • TI-2026-76780 Command injection in mcollina mcp-ripgrep Advanced Search Tool CVSS 4.0MEDIUM 4.8
  • TI-2026-69605 Truncated map32 headers throw RangeError in msgpack5 decoder CVSS 3.1HIGH 7.5
  • TI-2026-69603 msgpack5 streaming decoder recursion can exhaust the call stack CVSS 3.1HIGH 7.5
  • TI-2026-69599 Deeply nested input exhausts the stack in msgpack5 decoder CVSS 3.1MEDIUM 5.3
  • TI-2026-69606 Prototype pollution in msgpack5 with partial options CVSS 3.1MEDIUM 6.5
  • TI-2026-69609 Quadratic parsing in msgpack5 streaming decoder blocks the event loop CVSS 3.1MEDIUM 5.9
See all 7 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences