msgpack5: Decoding negative int64 values mutates the input buffer

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

3.7 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

• CVE-2026-107296: 0.28% estimated exploitation activity in the next 30 days; percentile 20.05 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Decoding a negative signed 64-bit integer modifies the corresponding bytes in the caller-provided input buffer. Applications that retain or reuse encoded input for integrity checks, logging, or subsequent processing may observe silently corrupted data. Positive integers and other MessagePack value types are not affected. Patches The decoder now computes signed 64-bit values without writing to the input buffer. Workarounds Copy untrusted MessagePack input before decoding it, or do not retain or reuse input buffers after decoding.

Published by the source

8 Oct 2026, 17:39 UTC

Last modified by the source

8 Oct 2026, 17:45 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-qw35-55vc-rhgj

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-qw35-55vc-rhgj

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-qw35-55vc-rhgj

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# Patch Next advisory brief: CVE-2026-107296

Advisory: msgpack5: Decoding negative int64 values mutates the input buffer
IDs: CVE-2026-107296, GHSA-qw35-55vc-rhgj
Record: https://patchnext.com/advisories/cve-2026-107296 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: msgpack5 6.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm msgpack5: affected < 6.1.0; fixed in 6.1.0

## Suggested inspection (read-only)
- `npm ls msgpack5 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on msgpack5.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qw35-55vc-rhgj (GitHub-reviewed advisory GHSA-qw35-55vc-rhgj lists affected ranges: npm msgpack5 >=0 <6.1.0)
- Verified: https://osv.dev/vulnerability/GHSA-qw35-55vc-rhgj (OSV record GHSA-qw35-55vc-rhgj lists affected ranges: npm msgpack5 >=0 <6.1.0 (fixed))

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