Undertow-core vulnerable to HTTP Request Smuggling

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2017-2666: 3.09% estimated exploitation activity in the next 30 days; percentile 87.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

19 Oct 2018, 16:55 UTC

Last modified by the source

9 Jan 2023, 05:03 UTC

Source last checked

26 Oct 2026, 15:53 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mcfm-h73v-635m

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# Patch Next advisory brief: CVE-2017-2666

Advisory: Undertow-core vulnerable to HTTP Request Smuggling
IDs: CVE-2017-2666, GHSA-mcfm-h73v-635m
Record: https://patchnext.com/advisories/cve-2017-2666 (revision 1, source checked 26 Oct 2026, 15:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.undertow:undertow-core 1.4.17, 1.3.31. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.undertow:undertow-core: affected < 1.3.31; >= 1.4.0, < 1.4.17; fixed in 1.4.17, 1.3.31

## Suggested inspection (read-only)
- Maven io.undertow:undertow-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.undertow:undertow-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-mcfm-h73v-635m (GitHub-reviewed advisory GHSA-mcfm-h73v-635m lists affected ranges: Maven io.undertow:undertow-core >=0 =1.4.0 <1.4.17)

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