Apache Tomcat up to 11.0.25/10.1.59/9.0.121/8.5.100 Transfer-Encoding expected behavior violation

Summaryinfo

A vulnerability labeled as critical has been found in Apache Tomcat up to 11.0.25/10.1.59/9.0.121/8.5.100. This affects an unknown function of the component Transfer-Encoding. Executing a manipulation can lead to expected behavior violation. This vulnerability is tracked as CVE-2026-77756. The attack can be launched remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Apache Tomcat up to 11.0.25/10.1.59/9.0.121/8.5.100. It has been declared as critical. This vulnerability affects an unknown part of the component Transfer-Encoding. The manipulation with an unknown input leads to a expected behavior violation vulnerability. The CWE definition for the vulnerability is CWE-440. A feature, API, or function does not perform according to its specification. As an impact it is known to affect integrity, and availability. CVE summarizes:

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.

The advisory is available at lists.apache.org. This vulnerability was named CVE-2026-77756 since 08/21/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 09/24/2026).

The vulnerability scanner Nessus provides a plugin with the ID 349588 (Linux Distros Unpatched Vulnerability : CVE-2026-77756), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 11.0.26, 10.1.60 or 9.0.122 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (349588) and CERT Bund (WID-SEC-2026-3527). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Apache Tomcat

Productinfo

Type

• Application Server Software

Vendor

• Apache

Name

• Tomcat

Version

• 8.0
• 8.1
• 8.2
• 8.3
• 8.4
• 8.5.100
• 9.0.121
• 10.1.0
• 10.1.1
• 10.1.2
• 10.1.3
• 10.1.4
• 10.1.5
• 10.1.6
• 10.1.7
• 10.1.8
• 10.1.9
• 10.1.10
• 10.1.11
• 10.1.12
• 10.1.13
• 10.1.14
• 10.1.15
• 10.1.16
• 10.1.17
• 10.1.18
• 10.1.19
• 10.1.20
• 10.1.21
• 10.1.22
• 10.1.23
• 10.1.24
• 10.1.25
• 10.1.26
• 10.1.27
• 10.1.28
• 10.1.29
• 10.1.30
• 10.1.31
• 10.1.32
• 10.1.33
• 10.1.34
• 10.1.35
• 10.1.36
• 10.1.37
• 10.1.38
• 10.1.39
• 10.1.40
• 10.1.41
• 10.1.42
• 10.1.43
• 10.1.44
• 10.1.45
• 10.1.46
• 10.1.47
• 10.1.48
• 10.1.49
• 10.1.50
• 10.1.51
• 10.1.52
• 10.1.53
• 10.1.54
• 10.1.55
• 10.1.56
• 10.1.57
• 10.1.58
• 10.1.59
• 11.0.0
• 11.0.1
• 11.0.2
• 11.0.3
• 11.0.4
• 11.0.5
• 11.0.6
• 11.0.7
• 11.0.8
• 11.0.9
• 11.0.10
• 11.0.11
• 11.0.12
• 11.0.13
• 11.0.14
• 11.0.15
• 11.0.16
• 11.0.17
• 11.0.18
• 11.0.19
• 11.0.20
• 11.0.21
• 11.0.22
• 11.0.23
• 11.0.24
• 11.0.25

License

• open-source

Website

• Vendor: https://www.apache.org/

CPE 2.3info

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CPE 2.2info

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CVSSv4info

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CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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