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CVE-2026-107297

msgpack5: Quadratic parsing in the streaming decoder

5.9 MediumFix available

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.39%Unchanged since Oct 9, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.9

msgpack5: Quadratic parsing in the streaming decoder

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Record
CVE-2026-107297
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-407
Updated
2026-11-02
EUVDEUVD-2026-95108 5.9

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Record
EUVD-2026-95108
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-gcx5-hxj7-gpqq 5.9

msgpack5: Quadratic parsing in the streaming decoder

Impact

The streaming decoder reparses an incomplete container from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack value across many small chunks, causing quadratic CPU usage and blocking the event loop.

Patches

The decoder now preserves incremental container state so completed elements are not parsed again when more input arrives.

Workarounds

Buffer each complete MessagePack value before decoding it, or limit the number of chunks accepted for a single value.

Record
GHSA-gcx5-hxj7-gpqq
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-407
Updated
2026-11-02
NVD 5.9

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Record
CVE-2026-107297
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-407
Updated
2026-11-02
OSV 5.9

msgpack5: Quadratic parsing in the streaming decoder

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Record
CVE-2026-107297
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-407
Updated
2026-11-02
OSVGHSA-gcx5-hxj7-gpqq 5.9

msgpack5: Quadratic parsing in the streaming decoder

Impact

The streaming decoder reparses an incomplete container from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack value across many small chunks, causing quadratic CPU usage and blocking the event loop.

Patches

The decoder now preserves incremental container state so completed elements are not parsed again when more input arrives.

Workarounds

Buffer each complete MessagePack value before decoding it, or limit the number of chunks accepted for a single value.

Record
GHSA-gcx5-hxj7-gpqq
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-407
Updated
2026-11-02
OSVAZL-106842 No score

CVE-2026-107297 affecting package msgpack 3.3.0-1

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Record
AZL-106842
Updated
2026-11-02
OSVCLSA-2026-1791806348 No score

TuxCare security update for msgpack5 (5 CVEs)

TuxCare rebuilt msgpack5 to address 5 CVEs. Fixed in 4.5.1-tuxcare.1.

Record
CLSA-2026-1791806348
Updated
2026-11-02
OSVCLSA-2026-1793302953 No score

TuxCare security update for msgpack5 (7 CVEs)

TuxCare rebuilt msgpack5 to address 7 CVEs. Fixed in 3.6.1-tuxcare.1.

Record
CLSA-2026-1793302953
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
msgpack5
npm
before 6.1.0
6.1.0
msgpack
Azure Linux:3
through 3.3.0-1 None known
msgpack5
TuxCare:npm
From an advisory covering 5 CVEs
4.5.1-tuxcare.0 up to 4.5.1-tuxcare.1, plus listed versions
4.5.1
4.5.1-tuxcare.1
msgpack5
TuxCare:npm
From an advisory covering 7 CVEs
3.6.1-tuxcare.0 up to 3.6.1-tuxcare.1, plus listed versions
3.6.1
3.6.1-tuxcare.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-107297 is a medium vulnerability (CVSS 5.9) in Mcollina Msgpack5, published October 8, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.39%, the 33rd percentile. Fixed in msgpack5 6.1.0.

References

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