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CVE-2026-40395

CVE-2026-40395

This page contains facts from public vulnerability sources. Check the original advisory before updating.

Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared VCL. The headerplus.write_req0() function from vmod_headerplus updates the underlying req0, which is normally the original read-only request from which req is derived (readable and writable from VCL). This is useful in the active VCL, after amending req, to prepare a refined req0 before switching to a different VCL with the return (vcl(<label>)) action. This is for example how the Varnish Controller operates shared VCL deployments. If the amended req contained too many header fields for req0, this would have resulted in a workspace overflow that would in turn trigger a panic and crash the Varnish Enterprise server. This could be used as a Denial of Service attack vector by malicious clients.

CVSS 4.0 · Medium · EPSS 0.2% · Fix available

Published
Updated

Stack: system

Affected products and versions

  • varnish enterprise

    Versions
    • ≥ 6.0.9r5, < 6.0.16r12: Affected (custom)

    Update to 6.0.16r12

  • varnish Ubuntu:14.04:LTS

    Versions
    • 3.0.4-1ubuntu1
    • 3.0.4-1ubuntu2
    • 3.0.5-1ubuntu2
    • 3.0.5-2
    • 3.0.5-2ubuntu0.1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:Pro:16.04:LTS

    Versions
    • 4.0.3-1
    • 4.1.0-1
    • 4.1.0-2
    • 4.1.1-1
    • 4.1.1-1ubuntu0.2
    • 4.1.1-1ubuntu0.2+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:Pro:18.04:LTS

    Versions
    • 5.0.0-7.1
    • 5.2.1-1
    • 5.2.1-1ubuntu0.1
    • 5.2.1-1ubuntu0.1+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:Pro:20.04:LTS

    Versions
    • 6.1.1-1
    • 6.2.1-2
    • 6.2.1-2ubuntu0.1~esm1
    • 6.2.1-2ubuntu0.1~esm2
    • 6.2.1-2ubuntu0.1
    • 6.2.1-2ubuntu0.2
    • 6.2.1-2ubuntu0.2+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:Pro:22.04:LTS

    Versions
    • 6.5.2-1
    • 6.6.1-1
    • 6.6.1-1ubuntu0.2
    • 6.6.1-1ubuntu0.2+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:24.04:LTS

    Versions
    • 7.1.1-1.1ubuntu1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:25.10

    Versions
    • 7.7.0-1
    • 7.7.0-2
    • 7.7.0-3
    • 7.7.3-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:26.10

    Versions
    • 7.7.3-1build1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • varnish Ubuntu:26.04:LTS

    Versions
    • 7.7.3-1
    • 7.7.3-1build1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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