How severe is CVE-2026-102600?

CVE-2026-102600 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-102600?

CVE-2026-102600 affects the following packages: @socket.io/cluster-engine (npm). Ecosystems affected: npm.

How do I fix CVE-2026-102600?

Update @socket.io/cluster-engine to 0.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-102600 is resolved across your whole dependency graph.

How do I detect CVE-2026-102600 in my npm dependencies?

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

How do I mitigate CVE-2026-102600 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-102600 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-102600 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-2026-102600?

CVE-2026-102600 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 29th 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-2026-102600?

CVE-2026-102600 is classified as Improper Input Validation (CWE-20), CWE-1321 (CWE-1321). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-102600 published, and has it been updated?

CVE-2026-102600 was published on September 29, 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

HIGH severity

CVE-2026-102600 — cluster-engine

HIGHFix: socketio/socket.io@830e364

CVE-2026-102600 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in @socket.io/cluster-engine. A fix is available for @socket.io/cluster-engine — see the affected versions and patch details below.

Socket.IO: Prototype Pollution via Unsafe Client Session Lookup

Also known asGHSA-wfpm-5gcm-94cg

Published

Sep 29, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 15, 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 CVE-2026-102600.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs29th percentile — riskier than 29% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2026-102600 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.

0other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@socket.io/cluster-enginenpm

243downloads / week

Description

Impact

This is a prototype pollution / improper client lookup vulnerability in @socket.io/cluster-engine.

Servers using @socket.io/cluster-engine may be impacted when attacker-controlled session IDs are processed in clustered deployments. A malicious client could use special property names such as __proto__, constructor, or other inherited object keys as a session identifier, causing the server to read properties from the object prototype chain instead of only real connected clients.

The impact is denial of service through process crash.

Applications not using @socket.io/cluster-engine are not affected by this specific issue.

Affected versions:

@socket.io/[email protected]

Patches

The issue was fixed in:

@socket.io/[email protected]

Workarounds

If upgrading immediately is not possible, users can reduce exposure by:

Rejecting or sanitizing suspicious session IDs before they reach the cluster engine.
Running the cluster engine behind trusted infrastructure that prevents arbitrary clients from crafting raw Engine.IO session-related requests.

These workarounds are defense-in-depth only. Upgrading to a patched version is recommended.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@socket.io/cluster-engine`	all versions	0.1.1`npm install @socket.io/cluster-engine@0.1.1`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @socket.io/cluster-engine, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @socket.io/cluster-engine to 0.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-102600 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Impact This is a **prototype pollution / improper client lookup** vulnerability in `@socket.io/cluster-engine`. Servers using `@socket.io/cluster-engine` may be impacted when attacker-controlled session IDs are processed in clustered deployments. A malicious client could use special property names such as `__proto__`, `constructor`, or other inherited object keys as a session identifier, causing the server to read properties from the object prototype chain instead of only real connected clients. The impact is **denial of service** through process crash. Applications not using `@socket.