Vulnerability Details CVE-2026-40395
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 11.5%
CVSS Severity
CVSS v3 Score 4.0
Products affected by CVE-2026-40395
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cpe:2.3:a:varnish-software:varnish_enterprise:6.0.11
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cpe:2.3:a:varnish-software:varnish_enterprise:6.0.12
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cpe:2.3:a:varnish-software:varnish_enterprise:6.0.13
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cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16