Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

• CISA KEV Not listed.
• EPSS 0.0044, the 38th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

1. 31 Oct 2026, 14:56 UTC First seen by agentprime
2. 31 Oct 2026, 14:56 UTC Confirmed by OSV

Sources

• GitHub Advisory Database: GHSA-f59h-q822-g45g
• OSV: GHSA-f59h-q822-g45g
• github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g
• nvd.nist.gov/vuln/detail/CVE-2026-52845
• access.redhat.com/security/cve/CVE-2026-52845
• bugzilla.redhat.com/show_bug.cgi?id=2491907
• github.com/caddyserver/caddy
• security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.