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% (84th 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% (84th 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% (84th 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:*:*:*:*:*:*:*:*

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Other CWE-287 (Improper Authentication) vulnerabilities

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