CVE-2021-28543

Varnish varnish-modules before 0.17.1 allows remote attackers to cause a
denial of service (daemon restart) in some configurations. This does not
affect organizations that only install the Varnish Cache product; however,
it is common to install both Varnish Cache and varnish-modules.
Specifically, an assertion failure or NULL pointer dereference can be
triggered in Varnish Cache through the varnish-modules header.append() and
header.copy() functions. For some Varnish Configuration Language (VCL)
files, this gives remote clients an opportunity to cause a Varnish Cache
restart. A restart reduces overall availability and performance due to an
increased number of cache misses, and may cause higher load on backend
servers.

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