CVE-2021-28543

HIGH
7.5
CVSS Score
Published: March 16, 2021 at 02:43 PM UTC
Updated: June 17, 2026 at 03:46 AM UTC
3 products affected across 2 vendorsFedoraVarnish ModulesVarnish Modules Klarlack

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Severity
HIGH7.5
Exploit prediction
EPSS 1%

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 0.17.1
Affected range stops below 0.17.1, so it looks safe — our inference, not a vendor statement
v < 0.17.1
Affected range stops below 0.17.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-476CWE-617

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