How severe is CVE-2026-107296?

CVE-2026-107296 has a CVSS score of 3.7/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-107296?

CVE-2026-107296 affects the following packages: msgpack5 (npm). Ecosystems affected: npm.

How do I fix CVE-2026-107296?

Update msgpack5 to 6.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-107296 is resolved across your whole dependency graph.

How do I detect CVE-2026-107296 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for msgpack5, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-107296 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-107296 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-107296 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-107296?

CVE-2026-107296 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 19th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-107296?

CVE-2026-107296 is classified as CWE-471 (CWE-471). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-107296 published, and has it been updated?

CVE-2026-107296 was published on October 8, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

LOW severity

CVE-2026-107296 — msgpack5

LOWFix: mcollina/msgpack5@82b7039

CVE-2026-107296 is a low-severity (CVSS 3.7) CWE-471 vulnerability in msgpack5. A fix is available for msgpack5 — see the affected versions and patch details below.

msgpack5: Decoding negative int64 values mutates the input buffer

Also known asGHSA-qw35-55vc-rhgj

Published

Oct 8, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-107296.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs19th percentile — riskier than 19% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-107296 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,415 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

📦msgpack5

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`msgpack5`	all versions	6.1.0`npm install msgpack5@6.1.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for msgpack5, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update msgpack5 to 6.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-107296 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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.