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CVE-2021-28543

No known exploitation. EPSS puts it in the 74th percentile. Fixed in 0.17.1.

CVSS 3.14.0MediumEPSS percentile74th1.5% chance in 30 daysCISA KEVNot listedNo confirmed exploitation
No public exploit knownFix0.17.1Upgrade to this build

Published Updated Sources: CVE.org, NVD

NVD CVE.org

What to do

Find your product and version, then upgrade to the build on the right.

  • Varnish-cache Varnish-modulesAffected: < 0.17.1Upgrade to: 0.17.1Stated by: NVD
  • Varnish-cache Varnish-modules KlarlackAffected: < 0.17.1Upgrade to: 0.17.1Stated by: NVD

Versions as the sources state them. Full version matrix after sign-in

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

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.

In plain language

No plain-language summary for this CVE yet.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS74th
CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

1.5% chance of exploitation activity in the next 30 days, which ranks it in the 74th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

6 events over 1927 days, from the signal feeds we watch.

  1. OpenVAS check added
  2. Patch availablerecord updated
  3. Publishedweakness classified, att&ck mapped

Affected products

And 1 more affected product. See all after sign-in

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L

Scored 4.0 by NVD.

How it is reached

  • Attack Vector NetworkExploitable remotely over the network without any special conditions
  • Attack Complexity HighRequires specific conditions like a race condition or non-default configuration
  • Privileges Required NoneNo authentication required — anyone can exploit this
  • User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

  • Scope ChangedThe exploit can affect other components (e.g. sandbox escape, host compromise from VM)

Impact if exploited

  • Confidentiality NoneNo confidentiality impact
  • Integrity NoneNo integrity impact
  • Availability LowReduced performance or intermittent disruption of service

Weaknesses

ATT&CK techniques

Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.

Sources

References in the record

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We'll flag the next CVE, public exploit or patch for Varnish-modules, not every advisory.