CVE-2020-27782: A flaw was found in the Undertow AJP connector

This month

HIGH 7.5REMOTEWATCHLISTDOWNGRADEMITIGATEDOWNGRADE

CVE-2020-27782 is a high-severity flaw (CVSS 7.5) affecting jboss fuse, openshift application runtimes, undertow. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in the Undertow AJP connector. Malicious requests and abrupt connection closes could be triggered by an attacker using query strings with non-RFC compliant characters resulting in a denial of service. The highest threat from this vulnerability is to system availability. This affects Undertow 2.1.5.SP1, 2.0.33.SP2, and 2.2.3.SP1.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.4% (top 28%)
CISA exploited list	No
Weakness	CWE-400
Published	2021-02-23
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: redhat

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-02-23 19:15 UTCPublished CVE record published
2026-06-17 03:09 UTCUpdated Record last modified

redhat jboss fuse DOWNGRADE

Affected: 6.0.0 · 7.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.0.0

1. Check installed version

apt-cache policy jboss-fuse || rpm -q jboss-fuse || jboss-fuse --version

2. No fixed release: DOWNGRADE to a release before 6.0.0 (Debian / Ubuntu)

apt-cache madison jboss-fuse sudo apt install jboss-fuse=<VERSION_BEFORE_6.0.0> sudo apt-mark hold jboss-fuse

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list jboss-fuse sudo dnf downgrade jboss-fuse-<VERSION_BEFORE_6.0.0> sudo dnf versionlock add jboss-fuse

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat openshift application runtimes MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy openshift-application-runtimes || rpm -q openshift-application-runtimes || openshift-application-runtimes --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat undertow DOWNGRADE

Affected: 2.0.33 sp2 · 2.1.5 sp1 · 2.2.3 sp1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.0.33

1. Check installed version

apt-cache policy undertow || rpm -q undertow || undertow --version

2. No fixed release: DOWNGRADE to a release before 2.0.33 (Debian / Ubuntu)

apt-cache madison undertow sudo apt install undertow=<VERSION_BEFORE_2.0.33> sudo apt-mark hold undertow

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list undertow sudo dnf downgrade undertow-<VERSION_BEFORE_2.0.33> sudo dnf versionlock add undertow

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-27782?

jboss fuse: downgrade or apply the listed mitigation; openshift application runtimes: mitigate or apply the listed mitigation; undertow: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-27782 being exploited?

CVE-2020-27782 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-27782 affect?

CVE-2020-27782 affects jboss fuse, openshift application runtimes, undertow. Severity is high (CVSS 7.5). A flaw was found in the Undertow AJP connector. Malicious requests and abrupt connection closes could be triggered by an attacker using query strings with non-RFC compliant characters resulting in a denial of service. The highest threat fro

How urgent is CVE-2020-27782?

Priority 54/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

JBoss and WildFly vulnerabilities · Red Hat OpenShift vulnerabilities

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References

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