What’s Vulnerable › Vulnerabilities
CVE-2026-40395
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-04-12 · updated 2026-10-26
- Weakness: CWE-770
Description
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.
Affected products
- varnish-software Varnish Enterprise: through 6.0.15; 6.0.16-r1, 6.0.16-r10, 6.0.16-r11, 6.0.16-r2, 6.0.16-r3, 6.0.16-r4 (+5)
References
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