CVE-2026-30851

HighPublic PoC

Published: 07 March 2026

Published

07 March 2026

Modified

11 March 2026

KEV Added

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Patch

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CVSS Score 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

EPSS Score 0.0002 5.5th percentile

Risk Priority 16 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-30851 is a high-severity Improper Authentication (CWE-287) vulnerability in Caddyserver Caddy. Its CVSS base score is 8.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 5.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and AC-3 (Access Enforcement).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploitation for Privilege Escalation (T1068) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly remediates the vulnerability by requiring timely patching of Caddy to version 2.11.2 or later to fix the forward_auth copy_headers flaw.

SI-10 Information Input Validation partial match

prevent

Requires validation of client-supplied HTTP headers to prevent injection of malicious identity data into forwarded authentication requests.

AC-3 Access Enforcement partial match

prevent

Enforces approved access authorizations, mitigating privilege escalation resulting from injected identities in the authentication flow.

MITRE ATT&CK Enterprise TechniquesAI

T1068 Exploitation for Privilege Escalation Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

attack.mitre.org →

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

Vulnerability in Caddy's forward_auth copy_headers allows client header injection for identity impersonation on a network-accessible server, directly enabling authenticated privilege escalation (T1068) via exploitation of a public-facing application (T1190).

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD 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.

Deeper analysisAI

CVE-2026-30851 is a vulnerability in Caddy, an extensible server platform that uses TLS by default. It affects versions from 2.10.0 up to but not including 2.11.2, specifically in the forward_auth directive's copy_headers feature, which fails to strip client-supplied headers. This flaw enables identity injection and privilege escalation, rated at a CVSS v3.1 base score of 8.1 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N) and linked to CWE-287 (Improper Authentication) and CWE-345 (Insufficient Verification of Data Authenticity).

An attacker requires low privileges (PR:L) to exploit this vulnerability over the network (AV:N) with low attack complexity (AC:L) and no user interaction (UI:N). Exploitation allows injection of client-supplied headers into forwarded authentication requests, enabling identity impersonation and privilege escalation. This results in high impacts on confidentiality (C:H) and integrity (I:H) without affecting availability (A:N), all within the unchanged scope (S:U).

The vulnerability has been patched in Caddy version 2.11.2. Security practitioners should upgrade to this version for mitigation. Additional details are available in the GitHub security advisory (GHSA-7r4p-vjf4-gxv4), issue tracker (#6610), and related pull requests (#6608, #7545).