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CVE-2026-27590

Caddyserver Caddy vulnerability

9.8 CRITICALPublic exploitEPSS 0.86%
  1. Published24 Feb 2026

Description

Caddy 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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Caddyserver Caddy< 2.11.1

Remediation

Fixed in
Caddyserver Caddy≥ 2.11.1

References

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Frequently asked

Is CVE-2026-27590 being actively exploited?

CVE-2026-27590 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.86%.

How severe is CVE-2026-27590?

CVE-2026-27590 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.86% probability of exploitation.

Which products are affected by CVE-2026-27590?

Affected products include Caddyserver Caddy.

How do I fix CVE-2026-27590?

Upgrade affected software to a fixed version, for example Caddyserver Caddy 2.11.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-27590 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.