# Caddy forward_auth copy_headers Does Not Strip Client-Supplied Headers, Allowing Identity Injection and Privilege Escalation

Advisory record · `GHSA-7r4p-vjf4-gxv4`

- **Identifiers:** `GHSA-7r4p-vjf4-gxv4` · `CVE-2026-30851` · `GO-2026-4639`
- **State:** Confirmed
- **Severity:** CVSS 8.1 High
- **Critical:** No
- **Weakness (CWE):** [CWE-287](https://cwe.mitre.org/data/definitions/287.html) · [CWE-345](https://cwe.mitre.org/data/definitions/345.html)
- **Tags:** [Authentication bypass](https://agentprime.io/advisories/tag/auth-bypass.md) · [CWE-345](https://agentprime.io/advisories/tag/cwe-345.md)
- **Published:** 6 Mar 2026
- **Updated:** 23 Mar 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 6 Mar 2026, 23:38 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy` (Go): affected `>=2.10.0, <2.11.2`; fixed in `2.11.2`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Caddy's reverseproxy module (Go github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy) versions 2.10.0 up to but not including 2.11.2 are affected. When forward_auth uses copy_headers and the auth service returns 200 without one of those headers, a client-supplied header with the same name is not removed and reaches the backend. An attacker holding any valid auth token can therefore forge identity headers such as X-User-Id and gain privileges. Upgrade to version 2.11.2, which fixes the issue.

Written 7 Nov 2026.

## 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

- 8.1 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0029, the 21st percentile, on 11 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:09 UTC: First seen by agentprime
- 31 Oct 2026, 15:09 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-7r4p-vjf4-gxv4)

## Sources

- [GitHub Advisory Database: GHSA-7r4p-vjf4-gxv4](https://github.com/advisories/GHSA-7r4p-vjf4-gxv4)
- [OSV: GHSA-7r4p-vjf4-gxv4](https://osv.dev/vulnerability/GHSA-7r4p-vjf4-gxv4)
- <https://github.com/caddyserver/caddy/security/advisories/GHSA-7r4p-vjf4-gxv4>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-30851>
- <https://github.com/caddyserver/caddy/issues/6610>
- <https://github.com/caddyserver/caddy/pull/6608>
- <https://github.com/caddyserver/caddy/pull/7545>
- <https://github.com/caddyserver/caddy>

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.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-7r4p-vjf4-gxv4>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-7r4p-vjf4-gxv4/>. Everything for agents: <https://agentprime.io/llms.txt>.