CVE-2026-77756 is a vulnerability in Apache Tomcat
Published on September 23, 2026
Apache Tomcat: Transfer-Encoding honored for HTTP/1.0 requests
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in Apache Tomcat caused by processing the transfer-encoding header for an HTTP/1.0 request may allow an attacker to cause one request from another user to fail when Tomcat is located behind a reverse proxy.
This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.25, from 10.1.0-M1 through 10.1.59, from 9.0.47 through 9.0.121.
The following versions were EOL at the time the CVE was created but are
known to be affected: from 8.5.67 through 8.5.100. Other unsupported versions may also be affected.
Users are recommended to upgrade to version 11.0.26, 10.1.60 or 9.0.122, which fix the issue.
Vulnerability Analysis
CVE-2026-77756 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 have no impact on confidentiality and integrity, and a small impact on availability.
Weakness Type
What is a HTTP Request Smuggling Vulnerability?
When malformed or abnormal HTTP requests are interpreted by one or more entities in the data flow between the user and the web server, such as a proxy or firewall, they can be interpreted inconsistently, allowing the attacker to "smuggle" a request to one device without the other device being aware of it.
CVE-2026-77756 has been classified to as a HTTP Request Smuggling vulnerability or weakness.
Products Associated with CVE-2026-77756
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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 9.0.47, <= 9.0.121 is affected.
- Version 8.5.67, <= 8.5.100 is affected.
- Before and including 7.0.109 is unaffected.