CVE-2021-28543HighMicrosoft CVSS 4.0CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

Microsoft security update for CVE-2021-28543 — cbl2 varnish-modules on CBL Mariner 2.0

Published
October 1, 2025
Last Modified
—

🔗 CVE IDs covered (1)

📋 Microsoft's advisory

EchelonGraph does not copy Microsoft's advisory page: its FAQ and remediation text are not shown here. Read the advisory on https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-28543. This page also shows what EchelonGraph holds for CVE-2021-28543, with the description from its CVE record, which the CVE Numbering Authority that assigned the CVE wrote: for a CVE Microsoft assigned, often in the words of Microsoft's own advisory.

🎯 Affected products1

  • cbl2 varnish-modules on CBL Mariner 2.0

✅ Updates Microsoft lists: 1 update

1 row: one per KB article or update, update type and fixed build. Their details are on Microsoft's advisory.

KB articleUpdateFixed build
—Security Update—

🧭 EchelonGraph on CVE-2021-28543

EchelonGraph score
7.5 HIGH
CISA KEV
Not listed
Fix status
A fix is available — apply it.

Description from the CVE record (CVE.org), as published by its numbering authority

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.

Published by MITRE Corporation, the CVE Numbering Authority that assigned CVE-2021-28543, in its CVE record at CVE.org; reused under the CVE Program's Terms of Use (its licence and MITRE's copyright notice are in our Terms of Service).

🔗 References (2)