CVE-2017-2666 Undertow-core vulnerable to HTTP Request Smuggling

What is CVE-2017-2666?

CVE-2017-2666 is a medium-severity cross-site scripting vulnerability in Debian Debian Linux, published on 27 Jul 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

It was discovered in Undertow that the code that parsed the HTTP request line permitted invalid characters. This could be exploited, in conjunction with a proxy that also permitted the invalid characters but with a different interpretation, to inject data into the HTTP response. By manipulating the HTTP response the attacker could poison a web-cache, perform an XSS attack, or obtain sensitive information from requests other than their own.

Weakness: CWE-444

Which versions are affected by CVE-2017-2666?

4 open source packages ship an affected version, including io.undertow:undertow-core. It affects 3 products.

Products include Debian Debian Linux, Redhat Jboss Enterprise Application Platform, Redhat Undertow.

How do I fix CVE-2017-2666?

Upgrade io.undertow:undertow-core to a fixed version for your release line: 1.3.31 or 1.4.17.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2017-2666 being exploited?

There is no known exploitation of CVE-2017-2666 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2017-2666, GHSA-mcfm-h73v-635m, UBUNTU-CVE-2017-2666.