How severe is GHSA-5x5g-h9x8-2fh9?

GHSA-5x5g-h9x8-2fh9 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-5x5g-h9x8-2fh9?

GHSA-5x5g-h9x8-2fh9 affects the following packages: msgpack5 (npm). Ecosystems affected: npm.

How do I fix GHSA-5x5g-h9x8-2fh9?

Update msgpack5 to 6.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-5x5g-h9x8-2fh9 is resolved across your whole dependency graph.

How do I detect GHSA-5x5g-h9x8-2fh9 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 GHSA-5x5g-h9x8-2fh9 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 GHSA-5x5g-h9x8-2fh9 actively exploited in the wild?

No public exploit code has been indexed for GHSA-5x5g-h9x8-2fh9 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 GHSA-5x5g-h9x8-2fh9?

GHSA-5x5g-h9x8-2fh9 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 36th 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 GHSA-5x5g-h9x8-2fh9?

GHSA-5x5g-h9x8-2fh9 is classified as CWE-674 (CWE-674). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-5x5g-h9x8-2fh9 published, and has it been updated?

GHSA-5x5g-h9x8-2fh9 was published on October 8, 2026 and was last updated on October 8, 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

HIGH severity

msgpack5: Many buffered values can exhaust the streaming decoder stackGHSA-5x5g-h9x8-2fh9

HIGHFix: mcollina/msgpack5@77fbef1

GHSA-5x5g-h9x8-2fh9 is a high-severity (CVSS 7.5) CWE-674 vulnerability in msgpack5. A fix is available for msgpack5 — see the affected versions and patch details below.

Also known asCVE-2026-107300

Published

Oct 8, 2026

Updated

Oct 8, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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 GHSA-5x5g-h9x8-2fh9.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs36th percentile — riskier than 36% of all scored CVEsHighest risk

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

How urgent is this, really

GHSA-5x5g-h9x8-2fh9 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 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

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

214other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

msgpack5npm

89Kdownloads / week

Description

Impact

The streaming decoder recursively invokes itself for every complete value remaining in a chunk. A single chunk containing many small valid MessagePack values can exhaust the JavaScript call stack and interrupt the process or stream.

Patches

The streaming decoder now drains concatenated values iteratively with constant call-stack depth.

Workarounds

Limit the number of MessagePack values accepted in one chunk, or split large batches before passing them to the decoder stream.

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 GHSA-5x5g-h9x8-2fh9 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 The streaming decoder recursively invokes itself for every complete value remaining in a chunk. A single chunk containing many small valid MessagePack values can exhaust the JavaScript call stack and interrupt the process or stream. ### Patches The streaming decoder now drains concatenated values iteratively with constant call-stack depth. ### Workarounds Limit the number of MessagePack values accepted in one chunk, or split large batches before passing them to the decoder stream.