CVE-2026-27586— Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
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I. Basic Information for CVE-2026-27586
Vulnerability Information
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Vulnerability Title
Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
Source: NVD (National Vulnerability Database)
Vulnerability Description
Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in `ClientAuthentication.provision()` cause mTLS client certificate authentication to silently fail open when a CA certificate file is missing, unreadable, or malformed. The server starts without error but accepts any client certificate signed by any system-trusted CA, completely bypassing the intended private CA trust boundary. Any deployment using `trusted_ca_cert_file` or `trusted_ca_certs_pem_files` for mTLS will silently degrade to accepting any system-trusted client certificate if the CA file becomes unavailable. This can happen due to a typo in the path, file rotation, corruption, or permission changes. The server gives no indication that mTLS is misconfigured. Version 2.11.1 fixes the vulnerability.
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
对异常条件的处理不恰当
Source: NVD (National Vulnerability Database)
Vulnerability Title
Caddy 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Caddy是Caddy公司的一款开源、跨平台的HTTP/Web服务器。 Caddy 2.11.1之前版本存在安全漏洞，该漏洞源于ClientAuthentication.provision函数中的两个被忽略的错误导致mTLS客户端证书身份验证静默失败，可能允许绕过预期的私有CA信任边界。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| caddyserver | caddy | < 2.11.1 | - |
II. Public POCs for CVE-2026-27586
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|---|
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- Release v2.11.1 · caddyserver/caddy · GitHubx_refsource_MISC
- https://nvd.nist.gov/vuln/detail/CVE-2026-27586
Same Patch Batch · caddyserver · 2026-02-24 · 6 CVEs total
| CVE-2026-27585 | Caddy's improper sanitization of glob characters in file matcher may lead to bypassing sec | |
| CVE-2026-27587 | Caddy: MatchPath %xx (escaped-path) branch skips case normalization, enabling path-based r | |
| CVE-2026-27588 | Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based r | |
| CVE-2026-27590 | Caddy: Unicode case-folding length expansion causes incorrect split_path index (SCRIPT_NAM | |
| CVE-2026-27589 | Caddy vulnerable to cross-origin config application via local admin API /load (caddy) |
IV. Related Vulnerabilities
Same product: caddy
- CVE-2026-30851
Caddy forward_auth copy_headers Does Not Strip Client-Suppli - CVE-2026-30852
Caddy: vars_regexp double-expands user input, leaking env va - CVE-2026-27590
Caddy: Unicode case-folding length expansion causes incorrec - CVE-2026-27589
Caddy vulnerable to cross-origin config application via loca - CVE-2026-27588
Caddy: MatchHost becomes case-sensitive for large host lists
Same vendor: caddyserver
- CVE-2026-30851
Caddy forward_auth copy_headers Does Not Strip Client-Suppli - CVE-2026-30852
Caddy: vars_regexp double-expands user input, leaking env va - CVE-2026-27590
Caddy: Unicode case-folding length expansion causes incorrec - CVE-2026-27589
Caddy vulnerable to cross-origin config application via loca - CVE-2026-27588
Caddy: MatchHost becomes case-sensitive for large host lists
Same weakness: CWE-755
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SvelteKit's invalidated redirect in handle hook causes Denia - CVE-2026-28542
Huawei EMUI和Huawei HarmonyOS 安全漏洞 - CVE-2026-27195
Wasmtime is vulnerable to panic when dropping a `[Typed]Func - CVE-2026-25957
Cube Denial of Service (DoS) - An authenticated attacker can
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