CVE-2026-77762
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Race Condition in Apache Tomcat HTTP/2 Request Handling

Publication date: 2026-09-23

Last updated on: 2026-09-23

Assigner: Apache Software Foundation

Description
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in Apache Tomcat allows an attacker to inject trailer fields into another HTTP/2 request. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.25, from 10.1.0-M1 through 10.1.59, from 9.0.39 through 9.0.121. The following versions were EOL at the time the CVE was created but are known to be affected: from 8.5.59 through 8.5.100. Other unsupported versions may also be affected. Users are recommended to upgrade to version 11.0.26, 10.1.60, 9.0.122, which fix the issue.

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Meta Information

Published
2026-09-23
Last Modified
2026-09-23
Generated
2026-09-24
AI Q&A
2026-09-23
EPSS Evaluated
N/A
NVD
CVE-2026-77762
EUVD
EUVD-2026-85227

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
apache tomcat From 11.0.0-M1 (inc) to 11.0.25 (inc)
apache tomcat From 10.1.0-M1 (inc) to 10.1.59 (inc)
apache tomcat From 9.0.39 (inc) to 9.0.121 (inc)
apache tomcat From 8.5.59 (inc) to 8.5.100 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-362 The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

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Executive Summary

This is a race condition vulnerability in Apache Tomcat where improper synchronization allows an attacker to inject trailer fields into another HTTP/2 request. This occurs due to concurrent execution using shared resources without proper controls.

Detection Guidance

Detecting this race condition vulnerability in Apache Tomcat requires monitoring HTTP/2 request handling and trailer field injection attempts. Check Tomcat logs for unusual trailer field patterns or concurrent request anomalies. Use network monitoring tools like Wireshark to inspect HTTP/2 traffic for unexpected trailer headers. Enable Tomcat's access logs with detailed request headers to identify suspicious sequences.

Impact Analysis

An attacker could exploit this to manipulate HTTP/2 requests, potentially leading to unauthorized access, data breaches, or service disruption. Systems using affected Tomcat versions are at risk.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by allowing unauthorized data access or manipulation through race conditions in HTTP/2 requests. Attackers may exploit this to inject malicious trailer fields, potentially leading to data breaches or unauthorized modifications, which are critical violations under these regulations.

Mitigation Strategies

Upgrade Apache Tomcat to version 11.0.26, 10.1.60, 9.0.122, or later to fix the race condition vulnerability.

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