Request failure via stale recycled-request marker
Published Sep 23, 2026 · Updated Sep 23, 2026
Denial of service in affected Apache Tomcat 9, 10, and 11 releases allows remote attackers to fail another user's HTTP/2 request. StreamProcessor leaves Request.NOTE_BAD_REQUEST set when recycling a pooled HTTP/2 request, so a later request can inherit the stale error marker. Exploitation is unauthenticated and timing-dependent; it interrupts one concurrent request rather than crashing the Tomcat process.
Summary
What happened
Denial of service in affected Apache Tomcat 9, 10, and 11 releases allows remote attackers to fail another user's HTTP/2 request. StreamProcessor leaves Request.NOTE_BAD_REQUEST set when recycling a pooled HTTP/2 request, so a later request can inherit the stale error marker. Exploitation is unauthenticated and timing-dependent; it interrupts one concurrent request rather than crashing the Tomcat process.
The record
- CVE
- CVE-2026-78437
- Published
- Sep 23, 2026
- Updated
- Sep 23, 2026
- Vendor
- The Apache Software Foundation
- Product
- Apache Tomcat
- Classifications
- T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 23, 2026CVE publishedPublication date reported by the CVE source.
- Sep 23, 2026Record 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.
- Affected versionversion=10.1.53 <=10.1.59
- Affected versionversion=11.0.19 <=11.0.25
- Affected versionversion=9.0.116 <=9.0.121
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
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.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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