CVE-2021-3859Network attack vector

Service interruption via mishandled HTTP/2 continuation frames

Published Aug 26, 2022 · Updated Aug 3, 2024

Denial of service in Red Hat Undertow before 2.2.15.Final allows remote attackers to interrupt HTTP/2 client requests. Http2Channel.parseFrame returned before consuming buffered CONTINUATION frames, leaving the client invocation waiting until its timeout expired. An HTTP/2 peer must cause a header block to span continuation frames; successful exploitation interrupts affected client calls without reported data access or modification.

CVSS severity7.5
High
EPSS probability1.64%
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 before 2.2.15.Final allows remote attackers to interrupt HTTP/2 client requests. Http2Channel.parseFrame returned before consuming buffered CONTINUATION frames, leaving the client invocation waiting until its timeout expired. An HTTP/2 peer must cause a header block to span continuation frames; successful exploitation interrupts affected client calls without reported data access or modification.

The record

CVE
CVE-2021-3859
Published
Aug 26, 2022
Updated
Aug 3, 2024
Vendor
Red Hat
Product
Undertow
Classifications
CWE-214, CWE-668, CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=Fixed in 2.2.15.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Red Hat · Undertowversion=Fixed in 2.2.15.Final

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-214Invocation of Process Using Visible Sensitive Information
CWE-668Exposure of Resource to Wrong Sphere
CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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