# CVE-2026-123863: Node.js is vulnerable to a remote HTTP/2 denial of service via a reachable assertion in Http2Session teardown

> Unauthenticated HTTP/2 clients can crash Node.js servers via a reachable assertion in session teardown; Node.js HTTP/2 operators should care.

- **Severity:** High 8.2 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** Yes
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** ALPINE-CVE-2026-123863, BELL-CVE-2026-123863, DEBIAN-CVE-2026-123863, GHSA-cwc7-c9hg-jq89, UBUNTU-CVE-2026-123863

## What is CVE-2026-123863?

CVE-2026-123863 is a high-severity denial of service vulnerability in nodejs node, published on 11 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A reachable assertion in Node.js HTTP/2 session teardown lets any unauthenticated client abort the server, over both TLS and cleartext. A client can arrange for an Http2Stream that still holds nghttp2-allocated header buffers to outlive its session: the stream is removed from the session's stream set but never detached, so when ~Http2Session() runs the memory accounting is nonzero and the CHECK_EQ(current_nghttp2_memory_, 0) assertion fails, terminating the process. The trigger needs only a default http2 server whose handler responds before the request body has ended, which is typical. It is a variant of CVE-2024-27983 that the earlier fix did not cover, because that fix only detached streams still tracked in the session. This vulnerability affects Node.js 26.x (since 26.9.0) and 24.x (since 24.22.0).

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-123863?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-123863?

Upgrade to a fixed version.

## Is CVE-2026-123863 being exploited?

There is no known exploitation of CVE-2026-123863 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123863 and fix it if it is affected.

What it is: CVE-2026-123863 is a high-severity denial of service vulnerability in nodejs node, published on 11 Nov 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-2026-123863 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: nodejs node. 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-2026-123863/ (Markdown: https://insights.sbomify.com/CVE-2026-123863/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123863
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123863
- OSV: https://osv.dev/vulnerability/CVE-2026-123863

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123863/
Summaries are generated and may contain mistakes; the official description above is the record.