CVE-2026-30851 Caddy forward_auth copy_headers Does Not Strip Client-Supplied Headers, Allowing Identity Injection and Privilege Escalation
Attackers can inject identity headers via forward_auth copy_headers to bypass authentication and escalate privileges in Caddy servers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-30851?
CVE-2026-30851 is a high-severity authentication bypass vulnerability in caddyserver caddy, published on 7 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Caddy is an extensible server platform that uses TLS by default. From version 2.10.0 to before version 2.11.2, forward_auth copy_headers does not strip client-supplied headers, allowing identity injection and privilege escalation. This issue has been patched in version 2.11.2.
Which versions are affected by CVE-2026-30851?
3 open source packages ship an affected version, including github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy and github.com/caddyserver/caddy/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy Go | From 2.10.0 | 2.11.2 |
github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy Go | From 2.10.0 | 2.11.2 |
github.com/caddyserver/caddy/v2 Go | From 2.10.0 | 2.11.2 |
Products include Caddyserver Caddy.
How do I fix CVE-2026-30851?
Upgrade github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy to 2.11.2 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-30851 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30851 exists.
Other vulnerabilities in caddyserver caddy
- CVE-2018-21246 Caddy vulnerable to Authentication Bypass due to mishandling of TLS client authentication
- CVE-2026-27590 Caddy: Unicode case-folding length expansion causes incorrect split_path index in FastCGI transport
- CVE-2026-27586 Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
- CVE-2026-45135 Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files
- CVE-2026-52845 Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Sources
Also known as GHSA-7r4p-vjf4-gxv4, GO-2026-4639, MINI-vgjr-gr3p-cpxf, MINI-whjx-8fpg-cgrw, UBUNTU-CVE-2026-30851.