CVE-2026-27588 is a critical vulnerability affecting Caddy server versions prior to 2.11.1. It allows attackers to bypass host-based routing and access controls by manipulating the case of the HTTP Host header when Caddy is configured with a large host list. With a CVSS score of 9.1 (CRITICAL), this network-exploitable vulnerability requires no privileges or user interaction and can lead to high confidentiality and integrity impacts. There is currently no evidence of active exploitation, public exploit code, or KEV listing, though it has garnered some community discussion.
| Vendor | Product | Version(s) | CPE |
|---|---|---|---|
>= 2.10.2, < 2.11.1CPE matchmatch criteria | cpe:2.3:a:caddyserver:caddy:*:*:*:*:*:*:*:* |
CVSS version used by this source: 4.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.
The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.