VulnerabilityModified

CVE-2021-28543

Varnish varnish-modules before 0.17.1 allows remote attackers to cause a denial of service (daemon restart) in some configurations.

HIGH 7.5EPSS 1.49%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (1.49%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 3.1: 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 1.49% probability · 74th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-476, CWE-617
Affected: varnish-cache/varnish-modules · varnish-cache/varnish-modules klarlack · fedoraproject/fedora
Source: cve@mitre.org

EPSS trend

EPSS 1.5% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.