CVE
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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 22.23.5, 24.22.3, 26.13.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 22.23.5, 24.22.3, 26.13.1.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 42/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
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.
Read the original 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.
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.
Read the source excerpt
“This vulnerability affects all users in active release lines: 22.x, 24.x, 26.x”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach17/20Affects Node.js (a widely deployed server, runtime, framework or database)
- Severity7.5/10CVSS 7.5
- No patch0/5No signal
What would change the score
- Would score about 87 if added to CISA KEV
- Would score about 82 if CISA's SSVC rates exploitation active
- Would score about 47 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 22.23.5, 24.22.3, 26.13.1.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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"}.Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- 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
Evidence 4
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 1
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123866
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: cve.now feed data
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: nodejs.org
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: cve.now feed data
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: nodejs.org
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: nodejs.org