CVE-2020-27782Network attack vector

Service interruption via malformed AJP query strings

Published Feb 23, 2021 · Updated Aug 4, 2024

Denial of service in Red Hat Undertow 2.0.33.SP2, 2.1.5.SP1, and 2.2.3.SP1 allows remote attackers to interrupt AJP-backed services. The AJP connector accepts non-RFC query-string characters copied unchecked by a front-end proxy, then closes the connection without a response and marks the backend node broken. An exposed AJP listener behind mod_jk or mod_proxy_ajp is required, and repeated crafted requests can interrupt service availability.

CVSS severity7.5
High
EPSS probability1.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Red Hat Undertow 2.0.33.SP2, 2.1.5.SP1, and 2.2.3.SP1 allows remote attackers to interrupt AJP-backed services. The AJP connector accepts non-RFC query-string characters copied unchecked by a front-end proxy, then closes the connection without a response and marks the backend node broken. An exposed AJP listener behind mod_jk or mod_proxy_ajp is required, and repeated crafted requests can interrupt service availability.

The record

CVE
CVE-2020-27782
Published
Feb 23, 2021
Updated
Aug 4, 2024
Vendor
Red Hat
Product
Undertow
Classifications
CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0.33.SP2
  2. Affected versionversion=2.1.5.SP1
  3. Affected versionversion=2.2.3.SP1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Red Hat · Undertowversion=2.0.33.SP2; version=2.1.5.SP1; version=2.2.3.SP1

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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