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CVE-2026-56848 – HTTP/2 Heap Use-After-Free Denial of Service – Node.js 22.x, 24.x, and 26.x

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Summary

CVE-2026-56848 is a heap use-after-free vulnerability in the HTTP/2 implementation of Node.js, disclosed in the July 29, 2026 Node.js security releases. It affects all active release lines (26.x, 24.x, and 22.x) and is rated HIGH severity (CVSS 7.5). A remote, unauthenticated attacker can exploit it to corrupt memory and crash the server, resulting in denial of service.

Technical details

  • Root cause: A re-entrancy flaw in Node.js HTTP/2 handling allows nghttp2_session_mem_send() to be called re-entrantly while nghttp2_session_mem_recv() is still executing, producing a heap use-after-free (CWE-416).
  • Trigger conditions: Applies to servers with HTTP/2 enabled; the condition is reached when the underlying nghttp2 library is triggered to send data while it is still processing received data.
  • Attack vector: Network — remotely reachable, requires no privileges and no user interaction.
  • Impact: Memory corruption leading to process crash and denial of service; code execution cannot be excluded in worst-case scenarios.

Affected software

  • Node.js 26.x up to and including 26.5.0
  • Node.js 24.x up to and including 24.18.0
  • Node.js 22.x up to and including 22.23.1

Severity

  • CVSS base score: 7.5 (HIGH)
  • Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Mitigation and recommended actions

  • Immediate: Upgrade to a patched release for your line — Node.js 26.5.1, 24.18.1, or 22.23.2. Users on End-of-Life versions should migrate to a supported release.
  • If no patch can be applied yet: Disable HTTP/2 where it is not required, or restrict/terminate HTTP/2 upstream of the Node.js process (for example, at a proxy or load balancer) to reduce exposure until patching.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Server response header: fastify
  • X-Powered-By response header: Express, fastify

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
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