How severe is CVE-2018-21246?

CVE-2018-21246 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2018-21246 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (86th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-21246?

CVE-2018-21246 affects Caddyserver Caddy. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-21246?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2018-21246 published?

CVE-2018-21246 was published on 2020-06-15 and last updated on 2026-06-17.

CVE-2018-21246

CVE-2018-21246 is a critical-severity vulnerability in Caddyserver Caddy with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (86th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-287
Affected product: Caddyserver Caddy
Published: 2020-06-15
Last modified: 2026-06-17

Description

Caddy before 0.10.13 mishandles TLS client authentication, as demonstrated by an authentication bypass caused by the lack of the StrictHostMatching mode.

Frequently asked questions

What is CVE-2018-21246?: Caddy before 0.10.13 mishandles TLS client authentication, as demonstrated by an authentication bypass caused by the lack of the StrictHostMatching mode.
How severe is CVE-2018-21246?: CVE-2018-21246 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2018-21246 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (86th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-21246?: CVE-2018-21246 affects Caddyserver Caddy. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-21246?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2018-21246 published?: CVE-2018-21246 was published on 2020-06-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:caddyserver:caddy:*:*:*:*:*:*:*:*

More vulnerabilities in Caddyserver Caddy

CVE-2026-27590 — Critical (CVSS 9.8): Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's FastCGI path…
CVE-2026-27588 — Critical (CVSS 9.1): Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request…
CVE-2026-27587 — Critical (CVSS 9.1): Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `path` request…
CVE-2026-27586 — Critical (CVSS 9.1): Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in…
CVE-2026-52845 — High (CVSS 8.1): Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the…
CVE-2026-45135 — High (CVSS 8.1): Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's…

All CVEs affecting Caddyserver Caddy →

Other CWE-287 (Improper Authentication) vulnerabilities

CVE-2026-101077 — Critical (CVSS 10.0): A flaw has been found in Netcore NR289-GE 1.4.5102. This impacts the function process_request of the component boa_temp…
CVE-2026-100886 — Critical (CVSS 10.0): A vulnerability was identified in Seetong T8108, T8108P, T8116 and T8232 4.6.1.4-build202604241011. The affected…
CVE-2026-77244 — Critical (CVSS 10.0): MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0,…
CVE-2026-94493 — Critical (CVSS 10.0): A vulnerability was detected in Gigatech PDV5701 1.0.31_240305_112640. This issue affects some unknown processing of…
CVE-2026-83099 — Critical (CVSS 10.0): Vulnerability in the Oracle Forms product of Oracle Fusion Middleware (component: Forms Services, C/S, Charmode).…
CVE-2026-83059 — Critical (CVSS 10.0): Vulnerability in the Oracle Internet Directory product of Oracle Fusion Middleware (component: OID LDAP Server).…

Browse all CWE-287 (Improper Authentication) vulnerabilities →