# CVE-2026-86040: libp2p: Unbounded RPC decode + synchronous subscription processing in @libp2p/floodsub allows unauthenticated DoS

> Remote attackers can cause CPU exhaustion and memory leaks in libp2p floodsub via unbounded RPC decoding, leading to node unavailability.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 17 Sep 2026
- **Updated:** 17 Sep 2026
- **Also known as:** GHSA-cvfg-hcf3-ggwv

## What is CVE-2026-86040?

CVE-2026-86040 is a high-severity denial of service vulnerability in @libp2p floodsub, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

libp2p is a JavaScript implementation of the libp2p networking stack. Prior to 11.0.26, @libp2p/floodsub accepts unauthenticated RPC frames on /floodsub/1.0.0 through PeerStreams.attachInboundStream in packages/floodsub/src/peer-streams.ts without protobuf element limits, then processRpc and processRpcSubOpt in packages/floodsub/src/floodsub.ts synchronously process the subscriptions array without a per-frame cap. A single bounded-size frame can decode into millions of empty subscription entries that block the event loop, while hundreds of thousands of unique-topic SUBSCRIBE entries allocate PeerSet objects in this.topics that are not removed after peer removal or stop. Empty entries cause CPU exhaustion but do not grow this.topics; persistent memory growth requires unique topics. The subscription path bypasses message signature validation and the message-only processing queue, allowing a remote peer to cause sustained CPU denial of service, memory exhaustion, out-of-memory termination, and node unavailability. The issue is fixed in version 11.0.26.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-401 (Missing Release of Memory after Effective Lifetime), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-86040?


## How do I fix CVE-2026-86040?

No fix has been published for CVE-2026-86040 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-86040 being exploited?

There is no known exploitation of CVE-2026-86040 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86040 and fix it if it is affected.

What it is: CVE-2026-86040 is a high-severity denial of service vulnerability in @libp2p floodsub, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-86040 in the wild and no public exploit code.

Affected product: @libp2p floodsub. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-86040/ (Markdown: https://insights.sbomify.com/CVE-2026-86040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86040
- OSV: https://osv.dev/vulnerability/CVE-2026-86040

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-86040/
Summaries are generated and may contain mistakes; the official description above is the record.