CVE-2026-27588· NVD / CVE Program· CNA GitHub_M

Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based route/auth bypass

Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.

HighCVSS 7.7 · v4.0—No exploit Fix available

Published: Feb 24, 2026
Updated: Jun 17, 2026
EPSS: 0.5% · 43th percentile
CWE: CWE-178

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Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.7 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.5%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 7.7; NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

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Affected systems

Vendor	Product	CPE
caddyserver	caddy	cpe:2.3:a:caddyserver:caddy

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

caddyserver caddy2.10.2 and later · before 2.11.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

caddyserver caddy
- < 2.11.1affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	caddy	all versions	—
Debian:13	caddy	before 2.6.2-12+deb13u1	2.6.2-12+deb13u1
Debian:14	caddy	before 2.11.2-1	2.11.2-1
Go	github.com/caddyserver/caddy/v2	before 2.11.1	2.11.1

Same product

caddyserver: all records

Other highest-scoring records for the same primary product.

CVE-2018-21246Caddy before 0.10.13 mishandles TLS client authentication, as demonstrated by an authentication bypass caused by the lack of the StrictHostM
40Plan
CVE-2026-30851Caddy forward_auth copy_headers Does Not Strip Client-Supplied Headers, Allowing Identity Injection and Privilege Escalation
35Monitor
CVE-2026-27590Caddy: Unicode case-folding length expansion causes incorrect split_path index (SCRIPT_NAME/PATH_INFO confusion) in FastCGI transport
35Monitor
CVE-2026-27586Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
35Monitor
CVE-2026-52845Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
32Monitor
CVE-2026-45135Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files
32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:caddy	2.6.2-12+deb13u1 · Debian:13	Package registry (OSV)
Go:github.com/caddyserver/caddy/v2	2.11.1	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-275870 days apartCaddy: MatchPath %xx (escaped-path) branch skips case normalization, enabling path-based route/auth bypass
30Monitor
CVE-2026-92700211 days apartCaddy: fileHidden() case-sensitive pattern bypass — exposes "hidden" files via case variation
25Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: X

Weakness class (CWE)

CWE-178 · Improper Handling of Case Sensitivity

CVSS vector

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

nvd-secondary