CVE-2026-77762 is a vulnerability in Apache Tomcat
Published on September 23, 2026
Apache Tomcat: Stale HPACK emitter injects trailers into recycled pooled Request
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.
Vulnerability Analysis
CVE-2026-77762 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
What is a Race Condition Vulnerability?
The program contains a code sequence that can run concurrently with other code, and the code sequence 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 that is operating concurrently.
CVE-2026-77762 has been classified to as a Race Condition vulnerability or weakness.
Products Associated with CVE-2026-77762
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Affected Versions
Apache Software Foundation Apache Tomcat:- Version 11.0.0-M1, <= 11.0.25 is affected.
- Version 10.1.0-M1, <= 10.1.59 is affected.
- Version 9.0.39, <= 9.0.121 is affected.
- Version 8.56.59, <= 8.5.100 is affected.
- Before and including 7.0.109 is unaffected.