critical CVSS 9 EPSS 0.49%

CVE-2026-56848·Node.js vulnerability

A flaw in Node.js HTTP/2 handling allows `nghttp2_session_mem_send()` to be called re-entrantly while `nghttp2_session_mem_recv()` is executing, resulting in a heap-use-after-free. This vulnerability affects Node.js **26.x**, **24.x**, and **22.x**.

Severity
critical
Software
Node.js
Fixed in
18.20.4+dfsg-1~deb12u3
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.49% — higher than 41% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-56848 scores 9 on CVSS, so a successful attack would be serious — but at 0.49%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 18.20.4+dfsg-1~deb12u3

Fixed in: 18.20.4+dfsg-1~deb12u3

How to fix this CVE

Update Node.js to version 18.20.4+dfsg-1~deb12u3 or later to patch a critical heap-use-after-free vulnerability in HTTP/2 session handling. This flaw can be triggered through concurrent HTTP/2 operations, leading to application crashes or potential memory corruption. Prioritize this update immediately due to the critical severity rating.

sudo dnf update nodejs

Defensia detects this vulnerability

How to check if you are affected

  1. Run `node --version` or `nodejs --version` to identify the currently installed Node.js version and compare against the fixed version 18.20.4+dfsg-1~deb12u3.
  2. Check if your application uses HTTP/2 by inspecting server configuration files (e.g., searching for h2 or spdy protocol declarations in reverse proxy configs like nginx or Apache).
  3. Search application logs for segmentation faults, memory access errors, or abrupt connection terminations that coincide with HTTP/2 traffic spikes using: `grep -i 'segmentation\|heap\|memory\|abort' /var/log/syslog /var/log/node*.log 2>/dev/null`.
  4. After patching, verify the fix by running `node --version` again and confirm it reports 18.20.4 or later, then restart the Node.js application and monitor for stable operation over 24 hours.

FAQ

What is CVE-2026-56848?

CVE-2026-56848 is a critical heap-use-after-free vulnerability in Node.js HTTP/2 processing where the nghttp2 session handler can be called re-entrantly, causing memory corruption when concurrent HTTP/2 operations occur simultaneously.

Is CVE-2026-56848 being actively exploited?

No, CVE-2026-56848 is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available, but the critical CVSS score warrants immediate patching.

What versions of Node.js are affected by CVE-2026-56848?

Node.js versions 26.x, 24.x, and 22.x are affected, along with earlier versions up to 18.20.4+dfsg-1~deb12u3 where the patch was released.

How do I check if my server is vulnerable to CVE-2026-56848?

Run `node --version` and verify the output. If it shows any version prior to 18.20.4+dfsg-1~deb12u3, or if you're running Node.js 22.x, 24.x, or 26.x, your system is vulnerable.

Does Defensia detect CVE-2026-56848?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Node.js is installed on a monitored server, CVE-2026-56848 will appear in your dashboard with remediation steps.

Related Node.js CVEs

CVE-2026-48930CVSS 10A flaw in Node.js TLS hostname handling can cause Embedded-nul hostnames can lead to silent authority rebinding due to c-string truncation in resolver bindings. This vulnerability affects all supported release lines: **Node.js 22**, **Node.js 24**, and **Node.js 26**.
CVE-2026-21636CVSS 10A flaw in Node.js's permission model allows Unix Domain Socket (UDS) connections to bypass network restrictions when `--permission` is enabled. Even without `--allow-net`, attacker-controlled inputs (such as URLs or socketPath options) can connect to arbitrary local sockets via net, tls, or undici/fetch. This breaks the intended security boundary of the permission model and enables access to privileged local services, potentially leading to privilege escalation, data exposure, or local code execution. * The issue affects users of the Node.js permission model on version v25. In the moment of this vulnerability, network permissions (`--allow-net`) are still in the experimental phase.
CVE-2025-55130CVSS 9.1A flaw in Node.js’s Permissions model allows attackers to bypass `--allow-fs-read` and `--allow-fs-write` restrictions using crafted relative symlink paths. By chaining directories and symlinks, a script granted access only to the current directory can escape the allowed path and read sensitive files. This breaks the expected isolation guarantees and enables arbitrary file read/write, leading to potential system compromise. This vulnerability affects users of the permission model on Node.js v20, v22, v24, and v25.
CVE-2026-48619CVSS 9A flaw in Node.js HTTP/2 client allows a server to send an unlimited number of ORIGIN frames, which could lead to an Out of Memory error on the client. This vulnerability affects all supported release lines: **Node.js 22**, **Node.js 24**, and **Node.js 26**.
CVE-2026-56846CVSS 9A flaw in Node.js HTTP/2 handling can cause HTTP/2 retained header blocks evade maxSessionMemory and enable remote memory exhaustion. This vulnerability affects Node.js **24.x** and **22.x**.

References

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