# CVE-2026-123864: Node.js is vulnerable to cross-connection memory disclosure via TLS write re-entrancy in the HTTPS request parser

> Unauthenticated clients can read other connections' memory, including TLS private keys, from Node.js HTTPS servers using certain request handling patterns.

- **Severity:** High 8.1 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:L/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:** Yes (`TLSWrap::DoWrite()`, `ClearOut()`, `llhttp_execute()`)
- **Fix available:** Yes
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** ALPINE-CVE-2026-123864, BELL-CVE-2026-123864, DEBIAN-CVE-2026-123864, GHSA-m526-rv55-w6mr, UBUNTU-CVE-2026-123864

## What is CVE-2026-123864?

CVE-2026-123864 is a high-severity use after free 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 re-entrancy flaw in Node.js HTTPS lets an unauthenticated client read memory belonging to other connections, including TLS private keys and other users' requests. TLSWrap::DoWrite() calls ClearOut() directly when asked to write zero bytes; if that write is issued from JavaScript running inside the HTTP parser's on_body callback, ClearOut() decrypts the next TLS record while the parser is still mid-body, re-entering llhttp_execute() and causing a use-after-free and an out-of-bounds heap read. The server then copies that freed or unrelated heap memory into the response for the request body. Triggering it requires a handler that calls res.flushHeaders() before the request body ends and later calls res.end() with a non-empty chunk, and reading the leaked memory requires any ordinary route that echoes or stores a request body. Cleartext node:http is not affected. This vulnerability affects Node.js 26.x, 24.x, and 22.x.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-123864?

An affected version is only exploitable if your software calls TLSWrap::DoWrite(), ClearOut() or llhttp_execute(). Many projects that include it are not exposed.


## How do I fix CVE-2026-123864?

No fix published yet.

## Is CVE-2026-123864 being exploited?

There is no known exploitation of CVE-2026-123864 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123864 and fix it if it is affected.

What it is: CVE-2026-123864 is a high-severity use after free 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-2026-123864 in the wild and no public exploit code.
Exposure: An affected version is only exploitable if your software calls TLSWrap::DoWrite(), ClearOut() or llhttp_execute(). Many projects that include it are not exposed.

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.
   If an affected version is present, also search the code for calls to TLSWrap::DoWrite(), ClearOut() or llhttp_execute() and report whether any exist.
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-2026-123864/ (Markdown: https://insights.sbomify.com/CVE-2026-123864/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123864
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123864
- OSV: https://osv.dev/vulnerability/CVE-2026-123864

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-123864/
Summaries are generated and may contain mistakes; the official description above is the record.