HighCVE-2026-78669

    Excessive CPU consumption from repeated initial window changes in net/http (CVE-2026-78669)

    Published Last modified Sources: Red Hat, SUSE, Ubuntu, Msrc Update Guide, OSV, CVE.org, BSI

    What is affected, what to do

    A flaw was found in the Go net/http package. This flaw allows a remote attacker to cause a Denial of Service (DoS) by triggering excessive CPU consumption on an affected client or server.

    Update Go standard library Net/http to version 1.26.9, Go standard library Net/http/internal/http2 to version 1.27.2, Golang.org/x/net/http2 to version 0.60.0.

    Affected
    • Go standard library Net/http lt *..1.26.9
    • Go standard library Net/http/internal/http2 lt 1.27.0-0..1.27.2
    • Golang.org/x/net/http2 lt *..0.60.0
    Fixed in
    • Go standard library Net/http 1.26.9
    • Go standard library Net/http/internal/http2 1.27.2
    • Golang.org/x/net/http2 0.60.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, SUSE, Ubuntu, Msrc Update Guide, OSV, CVE.org, BSI

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 49.2

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    86.87 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.6 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    49.2
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in the Go net/http package. This flaw allows a remote attacker to cause a Denial of Service (DoS) by triggering excessive CPU consumption on an affected client or server. By opening a large number of HTTP/2 streams and repeatedly sending small configuration (SETTINGS) frames that modify window sizes, an attacker forces the system into intensive state processing. This resource exhaustion degrades performance and can render the service unresponsive.

    Source: redhat_csaf, suse_csaf, Ubuntu Security Notices, Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Go standard librarynet/http
    • < 1.26.9
    • 1.26.9
    Go standard librarynet/http/internal/http2
    • 1.27.0-0 – < 1.27.2
    • 1.27.2
    golang.org/x/netgolang.org/x/net/http2
    • < 0.60.0
    • 0.60.0
    GolangGo
    • < 1.27.2
    • < 1.26.9
    • 1.27.2
    • 1.26.9
    gogolang.org/x/net
    • —
    • —
    gostdlib
    • —
    • 1.27.0-0
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntugolang-1.22focal
    Linuxubuntugolang-1.22jammy
    Linuxubuntugolang-1.22noble

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Weakness type: CWE-405

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
      Weakness type (CWE)added
      —
      CWE-405
      SSVC assessmentadded
      —
      {"id":"CVE-2026-78669","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-09T16:32:53.872432Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Receivedgolang.org

      Description added or changed

      Show 8 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      A malicious HTTP/2 peer can cause excessive CPU consumption in the client or server by opening a large number of streams and then sending many small SETTINGS frames containing SETTINGS_INITIAL_WINDOW_SIZE values.
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/78xxx/CVE-2026-78669.json">CVE-2026-78669</a>
      Referenceadded
      —
      https://go.dev/cl/847186
      Referenceadded
      —
      https://go.dev/cl/847308
      Referenceadded
      —
      https://go.dev/issue/81742
      Referenceadded
      —
      https://groups.google.com/g/golang-announce/c/U2fTuyDJznI
      Referenceadded
      —
      https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs
      Referenceadded
      —
      https://pkg.go.dev/vuln/GO-2026-6611

      Source identifier: security@golang.org

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