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Fencer Vulns
medium 4.8

CVE-2021-20220 json

HTTP request smuggling in Undertow

published 2021-02-23 5 y ago modified 2026-06-17 4 mo ago also GHSA-qjwc-v72v-fq6r , EUVD-2021-1382

cvss
4.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits
0
none known

Summary

A flaw was found in Undertow. A regression in the fix for CVE-2020-10687 was found. HTTP request smuggling related to CVE-2017-2666 is possible against HTTP/1.x and HTTP/2 due to permitting invalid characters in an HTTP request. This flaw allows an attacker to poison a web-cache, perform an XSS attack, or obtain sensitive information from request other than their own. The highest threat from this vulnerability is to data confidentiality and integrity.

Patch / fix

  • maven io.undertow:undertow-core 2.0.34, 2.1.6
  • redhat undertow 2.0.34, 2.1.6
  • undertow Debian 14 2.2.0-1

debian advisories DEBIAN-CVE-2021-20220

  • eap7-guava jboss enterprise application platform 7.3 30.1.0-1.redhat_00001.1.el7eap
  • eap7-wildfly jboss enterprise application platform 7.3 7.3.6-1.GA_redhat_00002.1.el7eap
  • eap7-narayana jboss enterprise application platform 7.3 5.9.11-1.Final_redhat_00001.1.el7eap
  • eap7-undertow jboss enterprise application platform 7.3 2.0.34-1.SP1_redhat_00001.1.el7eap
  • eap7-hal-console jboss enterprise application platform 7.3 3.2.13-1.Final_redhat_00001.1.el7eap
  • eap7-ironjacamar jboss enterprise application platform 7.3 1.4.27-1.Final_redhat_00001.1.el7eap
  • eap7-bouncycastle jboss enterprise application platform 7.3 1.68.0-1.redhat_00001.1.el7eap
  • eap7-jboss-remoting jboss enterprise application platform 7.3 5.0.20-2.SP1_redhat_00001.1.el7eap

red hat advisories RHSA-2021:0873RHSA-2021:0874RHSA-2021:0872

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20220 updated cvss 4.8

undertow: Possible regression in fix for CVE-2020-10687

  • Red Hat JBoss Data Grid 7 wildfly-undertow
    affected: no fix planned “Out of support scope”
  • Red Hat JBoss Enterprise Application Platform Expansion Pack wildfly-undertow
    affected: no fix available
  • Red Hat JBoss Fuse 6 undertow undertow
    affected: no fix planned “Out of support scope”
  • Red Hat OpenShift Application Runtimes wildfly-undertow
    affected: no fix available
  • Red Hat EAP-XP 2.0.0 via EAP 7.3.x base
    fixed: vendor fix RHSA-2021:2755
  • Red Hat EAP-XP via EAP 7.3.x base
    fixed: vendor fix RHSA-2021:2210
  • Red Hat JBoss EAP 7.3 for BaseOS-8 eap7-guava 30.1.0-1.redhat_00001.1.el8eap, eap7-wildfly 7.3.6-1.GA_redhat_00002.1.el8eap, eap7-bouncycastle 1.68.0-1.redhat_00001.1.el8eap, eap7-undertow 2.0.34-1.SP1_redhat_00001.1.el8eap, eap7-narayana 5.9.11-1.Final_redhat_00001.1.el8eap, eap7-activemq-artemis 2.9.0-9.redhat_00019.1.el8eap, +75 more
    fixed: vendor fix RHSA-2021:0874
  • Red Hat JBoss EAP 7.3 for RHEL 6 Server eap7-guava 30.1.0-1.redhat_00001.1.el6eap, eap7-wildfly 7.3.6-1.GA_redhat_00002.1.el6eap, eap7-bouncycastle 1.68.0-1.redhat_00001.1.el6eap, eap7-undertow 2.0.34-1.SP1_redhat_00001.1.el6eap, eap7-narayana 5.9.11-1.Final_redhat_00001.1.el6eap, eap7-activemq-artemis 2.9.0-9.redhat_00019.1.el6eap, +75 more
    fixed: vendor fix RHSA-2021:0872
show 4 more
  • Red Hat JBoss EAP 7.3 for RHEL 7 Server eap7-guava 30.1.0-1.redhat_00001.1.el7eap, eap7-wildfly 7.3.6-1.GA_redhat_00002.1.el7eap, eap7-bouncycastle 1.68.0-1.redhat_00001.1.el7eap, eap7-undertow 2.0.34-1.SP1_redhat_00001.1.el7eap, eap7-narayana 5.9.11-1.Final_redhat_00001.1.el7eap, eap7-activemq-artemis 2.9.0-9.redhat_00019.1.el7eap, +77 more
    fixed: vendor fix RHSA-2021:0873
  • Red Hat JBoss Enterprise Application Platform 7
    fixed: vendor fix RHSA-2021:0885
  • Red Hat Single Sign-On 7.4.6
    fixed: vendor fix RHSA-2021:0974
  • Red Hat Decision Manager 7 undertow undertow Red Hat Fuse 7 undertow undertow Red Hat Process Automation 7 wildfly-undertow
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.20% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N
GitHub 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
maven io.undertow:undertow-core
>=2.1.0, <2.1.6
<2.0.34
2.1.6
2.0.34

Affected products

  • n/a undertow

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.