Summaryinfo

A vulnerability labeled as critical has been found in Undertow. This impacts an unknown function of the component HTTP Request Handler. The manipulation results in request smuggling. This vulnerability is known as CVE-2026-28369. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability, which was classified as critical, was found in Undertow (the affected version unknown). Affected is an unknown part of the component HTTP Request Handler. The manipulation with an unknown input leads to a request smuggling vulnerability. CWE is classifying the issue as CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

A flaw was found in Undertow. When Undertow receives an HTTP request where the first header line starts with one or more spaces, it incorrectly processes the request by stripping these leading spaces. This behavior, which violates HTTP standards, can be exploited by a remote attacker to perform request smuggling. Request smuggling allows an attacker to bypass security mechanisms, access restricted information, or manipulate web caches, potentially leading to unauthorized actions or data exposure.

The advisory is shared for download at access.redhat.com. This vulnerability is traded as CVE-2026-28369 since 02/27/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 03/31/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-0907). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Red Hat Undertow

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Name

• Undertow

License

• free

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• 🔒

CPE 2.2info

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