CVE-2026-27586: caddyserver caddy
Vulnerability summary
CVE-2026-27586 is a critical (CVSS 9.1) vulnerability in caddyserver caddy. EPSS estimates a 0.40% chance of exploitation in the next 30 days, higher than 32.5% of scored vulnerabilities. 2 public exploits are recorded.
Advisory lineage
Upstream 0 · Downstream 2 · Related 2Timeline
- 24-02-2026PublishedVulnerability first disclosed.
- 26-02-2026Last modifiedVulnerability information updated.
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.
CVSS metrics
7 scores · 5 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:PDiffers
- OSV · GoEcosystem advisory · calculated9.3CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:PDiffers
- NVDNIST8.8HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/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
- OSV · UbuntuEcosystem advisory · calculated9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- OSV · DebianEcosystem advisory · calculated9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS trend
Probability
0.40%
Chance of exploitation in the next 30 days
Percentile
33%
Versus all other CVEs
30-day change
+0.13 pp
From 0.27% on 20-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
2 foundCaddy
Maturity: poc
9566C79C76C0B64C57F8Bd0716F97C48
Maturity: poc
Weaknesses
CWE · root causeAffected systems
Caddyserver1 product
- caddy< 2.11.1
Debian1 product
- caddy< 2.11.2-1
Github.com/caddyserver/caddy1 product
- v2< 2.11.1
Ubuntu1 product
- caddyAll versions (No fix recorded)
4 vendors · 4 products
References
10 links- github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7X Refsource CONFIRMREPORTWEBAdvisoryExploitVendor Advisory
- github.com/caddyserver/caddyPACKAGE