CVE-2021-28169: For Eclipse Jetty versions <= 9.4.40, <= 10.0.2, <= 11.0.2, it is possible for requests to the ConcatServlet with a d…

Is it exploited?

Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of 29 Oct 2026.

VulnCheck KEV lists it since 19 Aug 2022. It cites 2 public reports, the first from 19 Aug 2022.

• unit42.paloaltonetworks.com
• app.crowdsec.net

How likely is exploitation in the next 30 days?

78.5%

EPSS score, percentile 99.6 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

5.3 Medium

CVSS v3.1 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (1)

Which versions are affected?

Affected

• 9.4.40 and earlier
• 10.0.2 and earlier
• 11.0.2 and earlier

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; VulnCheck KEV, as of 30 Oct 2026; FIRST EPSS, as of 30 Oct 2026; CVE List, as of 30 Oct 2026. About the data.

Description

For Eclipse Jetty versions <= 9.4.40, <= 10.0.2, <= 11.0.2, it is possible for requests to the ConcatServlet with a doubly encoded path to access protected resources within the WEB-INF directory. For example a request to `/concat?/%2557EB-INF/web.xml` can retrieve the web.xml file. This can reveal sensitive information regarding the implementation of a web application.

Source: CVE List, as of 30 Oct 2026. About the data.

What to do

Advisories and patches

• DSA-4949 (Vendor advisory)

This summary is based on the CVE record as of 30 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

Source: CVE List, as of 30 Oct 2026. About the data.

Timeline