caddy: Improper Authentication
CVE-2026-30851 is a high-severity improper authentication vulnerability in caddy from Caddyserver, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected caddy versions: >= 2.10.0, < 2.11.2. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of caddy you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Caddyserver | caddy | >= 2.10.0, < 2.11.2 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.1 | High | CNA (github.com) |
| CVSS 3.1 | 8.8 | High | NVD |
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
How developers prevent this class of flaw
- Use an authentication framework or library such as the OWASP ESAPI Authentication feature.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/caddyserver/caddy/security/advisories/GHSA-7r4p-vjf4-gxv4Exploit, Mitigation
Patches and release notes
- github.com/caddyserver/caddy/pull/6608Issue Tracking
- github.com/caddyserver/caddy/pull/7545Issue Tracking
Other references
- github.com/caddyserver/caddy/issues/6610Issue Tracking
Other vulnerabilities in caddy
- 8.1 High severity
- 7.5 High severity
- 8.1 High severity
- 7.5 High severity
- 9.8 Critical severity
- 9.1 Critical severity
Recent Improper Authentication vulnerabilities
- 8.2 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.0 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
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