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CVE-2026-52845

Caddyserver Caddy authentication bypass

8.1 HIGHPublic exploitEPSS 0.45%
  1. Published23 Jun 2026

Description

Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _. This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Affected products

Caddyserver Caddy< 2.11.4

Remediation

Fixed in
Caddyserver Caddy≥ 2.11.4

References

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Frequently asked

Is CVE-2026-52845 being actively exploited?

CVE-2026-52845 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.45%.

How severe is CVE-2026-52845?

CVE-2026-52845 has a CVSS 3.1 base score of 8.1, rated high. EPSS estimates a 0.45% probability of exploitation.

Which products are affected by CVE-2026-52845?

Affected products include Caddyserver Caddy.

How do I fix CVE-2026-52845?

Upgrade affected software to a fixed version, for example Caddyserver Caddy 2.11.4 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-52845 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.