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

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

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.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-123863 being exploited?

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

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2026-123863, BELL-CVE-2026-123863, DEBIAN-CVE-2026-123863, GHSA-cwc7-c9hg-jq89, UBUNTU-CVE-2026-123863.