CaddyWeb server / proxy · Caddyserver
CVE-2026-27590
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedCaddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's FastCGI path splitting logic computes the split index on a lowercased copy of the request path and then uses that byte index to slice the original path. This is unsafe for Unicode because `strings.ToLower()` can change UTF-8 byte length for some characters. As a result, Caddy can derive an incorrect `SCRIPT_NAME`/`SCRIPT_FILENAME` and `PATH_INFO`, potentially causing a request that contains `.php` to execute a different on-disk file than intended (path confusion). In setups where an attacker can control file contents (e.g., upload features), this can lead to unintended PHP execution of non-.php files (potential RCE depending on deployment). Version 2.11.1 fixes the issue.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn Caddy versions before 2.11.1, the FastCGI path splitting logic computes the split index on a lowercased copy of the request path but applies that byte index to slice the original path. Since strings.ToLower() can change UTF-8 byte lengths for certain Unicode characters, this causes incorrect SCRIPT_NAME/SCRIPT_FILENAME and PATH_INFO values, enabling path confusion attacks where .php requests may execute unintended files.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
CaddyWeb server / proxy
< 2.11.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check Caddy versionRun `caddy version` to obtain the installed version numberAffected if The version is below 2.11.1 (e.g., 2.11.0, 2.10.x, etc.)
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Identify FastCGI PHP configurationInspect the Caddyfile or JSON config for the `php_fastcgi` directiveAffected if The php_fastcgi directive is present and handles .php requests
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Check for Unicode path handlingReview access logs for requests containing non-ASCII Unicode characters in the URL path (e.g., internationalized domain names or paths with accented characters)Affected if The server processes URLs with Unicode characters alongside php_fastcgi handling PHP files
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Inspect FastCGI SCRIPT_NAME valuesEnable debug logging and examine FastCGI parameters sent to PHP backend. Look for mismatches between requested URL path and SCRIPT_NAME/PATH_INFO valuesAffected if The SCRIPT_NAME or PATH_INFO values do not match the expected file path from the request
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Review for unexpected PHP executionCheck access and error logs for PHP file executions that do not correspond to the expected file structure or appear to bypass intended path restrictionsAffected if PHP files are being executed from locations not intended by the application logic
You are affected if running Caddy version below 2.11.1 with php_fastcgi configured and handling requests that contain Unicode characters in the URL path, leading to potential path confusion in FastCGI parameter handling.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2.11.1
Upgrade Caddy to version 2.11.1 or later. In deployments with file upload capabilities, audit uploaded content and restrict PHP execution to explicitly intended directories.
2.11.1
- Upgrade Caddy to version 2.11.1 or later
- Verify the upgrade by running 'caddy version' to confirm the installed version is 2.11.1 or higher
- Test FastCGI/PHP deployments to ensure path handling works correctly with Unicode characters
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Caddy
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-27590 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-27590 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data