Incorrect Behavior Order: Validate Before Canonicalize Affecting github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy/fastcgi package, versions <2.11.0
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMCADDYSERVERCADDYV2MODULESCADDYHTTPREVERSEPROXYFASTCGI-15364937
- published28 Feb 2026
- disclosed24 Feb 2026
- creditKevin Dunglas
Introduced: 24 Feb 2026
CVE-2026-27590 Â (opens in a new tab)How to fix?
Upgrade github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy/fastcgi to version 2.11.0 or higher.
Overview
Affected versions of this package are vulnerable to Incorrect Behavior Order: Validate Before Canonicalize via the splitPos function. An attacker can cause unintended execution of files by crafting URLs with specific Unicode characters that manipulate the path splitting logic, potentially leading to execution of attacker-controlled files.