{
  "threat_severity" : "Moderate",
  "public_date" : "2026-04-12T19:17:34Z",
  "bugzilla" : {
    "description" : "Varnish Cache: Varnish Enterprise: Varnish Cache and Varnish Enterprise: Denial of Service via workspace overflow",
    "id" : "2457695",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2457695"
  },
  "cvss3" : {
    "cvss3_base_score" : "5.9",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
    "status" : "draft"
  },
  "cwe" : "CWE-131",
  "details" : [ "Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a \"workspace overflow\" denial of service (daemon panic) for certain amounts of prefetched data. The setup of an HTTP/2 session starts with a speculative HTTP/1 transport, and upon upgrading to h2 the HTTP/1 request is repurposed as stream zero. During the upgrade, a buffer allocation is made to reserve space to send frames to the client. This allocation would split the original workspace, and depending on the amount of prefetched data, the next fetch could perform a pipelining operation that would run out of workspace.", "A flaw was found in Varnish Cache and Varnish Enterprise. A remote attacker can trigger a denial of service by sending specific amounts of prefetched data during an HTTP/2 session upgrade. This vulnerability, known as a \"workspace overflow,\" occurs when the system attempts to allocate a buffer, splitting the available memory workspace. Subsequent data processing then exhausts this limited workspace, causing the Varnish daemon to panic and become unavailable." ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "fix_state" : "Not affected",
    "package_name" : "varnish",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Not affected",
    "package_name" : "varnish:6/varnish",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Not affected",
    "package_name" : "varnish",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2026-40394\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-40394\nhttps://docs.varnish-software.com/security/VEV00002/" ],
  "name" : "CVE-2026-40394",
  "csaw" : false
}