CVE-2025-53506Network attack vector

Denial of service via deferred HTTP/2 limits

Published Jul 10, 2025 · Updated Nov 4, 2025

Uncontrolled resource consumption in Apache Tomcat allows remote attackers to interrupt service through an HTTP/2 connection. Http2UpgradeHandler deferred the configured maximum-concurrent-stream and initial-window limits until receipt of a SETTINGS acknowledgment, so a client withholding that acknowledgment could open streams without the intended initial limits taking effect. HTTP/2 must be enabled on the connector; exploitation requires no authentication or user interaction and can exhaust resources until the Tomcat service becomes unavailable.

CVSS severity7.5
High
EPSS probability1.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in Apache Tomcat allows remote attackers to interrupt service through an HTTP/2 connection. Http2UpgradeHandler deferred the configured maximum-concurrent-stream and initial-window limits until receipt of a SETTINGS acknowledgment, so a client withholding that acknowledgment could open streams without the intended initial limits taking effect. HTTP/2 must be enabled on the connector; exploitation requires no authentication or user interaction and can exhaust resources until the Tomcat service becomes unavailable.

The record

CVE
CVE-2025-53506
Published
Jul 10, 2025
Updated
Nov 4, 2025
Vendor
The Apache Software Foundation
Product
Apache Tomcat
Classifications
CWE-400, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 10, 2025CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record 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=10.1.0-M1 <=10.1.42
  2. Affected versionversion=11.0.0-M1 <=11.0.8
  3. Affected versionversion=8.5.0 <=8.5.100
  4. Affected versionversion=9.0.0.M1 <=9.0.106

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Tomcatversion=10.1.0-M1 <=10.1.42; version=11.0.0-M1 <=11.0.8; version=8.5.0 <=8.5.100; version=9.0.0.M1 <=9.0.106

Published CVSS scores

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 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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