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VulnerabilityPublished

CVE-2026-40395: Varnish Enterprise · Unthrottled Resource Allocation

Affects Varnish EnterpriseSource CVE Database V5

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Not known to be exploited · CVSS 4.0 Medium : upgrade to 6.0.16r12 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
4.0Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 14% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 6.0.16r12
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 12 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Varnish Enterprise to 6.0.16r12.

Affected software

ProductAffectedFixed in
varnish-softwareVarnish EnterpriseAffected
  • >=6.0.9r5 <6.0.16r12
Fixed in
  • 6.0.16r12

AI-suggested

If you cannot patch yet, consider limiting exposure of the vulnerable service to untrusted clients and monitor for unusual request patterns that might trigger the overflow.

Description

Varnish Enterprise versions before 6.0.16r12 contain a vulnerability where the headerplus.write_req0() function can cause a workspace overflow leading to a daemon panic and server crash. This occurs when an amended request contains too many header fields, triggering a denial of service condition. The issue affects shared VCL deployments and can be exploited by malicious clients to disrupt service availability.

References

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