Back to board Open MSRC
MSRC compact vulnerability detail

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.

No description was published by MSRC.

Severity
n/a
Impact
n/a
CVSS
4.0 base · 4.0 temporal
Release
2025-10-01
Signals
Mariner Unknown impact Exploited: n/a Publicly disclosed: n/a Exploitability: n/a
CWE
No CWE data published.
Patch Diff
Loading module diff metadata...
Resolved binary override
Use this when the MSRC module name cannot be mapped automatically or the resolved binary looks wrong.
Old version New version
Description
No description was published by MSRC.
FAQ / Articles
FAQ
Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by this vulnerability? One of the main benefits to our customers who choose to use the Azure Linux distro is the commitment to keep it up to date with the most recent and most secure versions of the open source libraries with which the distro is composed. Microsoft is committed to transparency in this work which is why we began publishing CSAF/VEX in October 2025. See this blog post for more information. If impact to additional products is identified, we will update the CVE to reflect this.