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Caddy is vulnerable to cross-origin config application via local admin API /load

Moderate severity GitHub Reviewed Published Feb 23, 2026 in caddyserver/caddy • Updated Feb 27, 2026

Package

gomod github.com/caddyserver/caddy/v2 (Go)

Affected versions

< 2.11.1

Patched versions

2.11.1

Description

commit: e0f8d9b2047af417d8faf354b675941f3dac9891 (as-of 2026-02-04)
channel: GitHub security advisory (per SECURITY.md)

summary

The local caddy admin API (default listen 127.0.0.1:2019) exposes a state-changing POST /load endpoint that replaces the entire running configuration.

When origin enforcement is not enabled (enforce_origin not configured), the admin endpoint accepts cross-origin requests (e.g., from attacker-controlled web content in a victim browser) and applies an attacker-supplied JSON config. this can change the admin listener settings and alter HTTP server behavior without user intent.

Severity

Medium

Justification:

  • The attacker can apply an arbitrary caddy config (integrity impact) by driving a victim’s local admin API.
  • Exploitation requires a victim running caddy with the admin API enabled and visiting an attacker-controlled page (or otherwise issuing the request from an untrusted local client).

Affected component

Reproduction

Attachment: poc.zip (integration harness) with canonical and control runs.

unzip -q -o poc.zip -d poc
cd poc/poc-F-CADDY-ADMIN-LOAD-001
make test

Expected output (excerpt):

[CALLSITE_HIT]: adminLoad.handleLoad
[PROOF_MARKER]: http_code=200 admin_moved=true response_pwned=true

Control output (excerpt):

[NC_MARKER]: http_code=403 load_blocked=true admin_moved=false response_pwned=false

Impact

An attacker can replace the running caddy configuration via the local admin API. Depending on the deployed configuration/modules, this can:

  • Change admin listener settings (e.g., move the admin listener to a new address)
  • Change HTTP server behavior (e.g., alter routes/responses)

Suggested remediation

Ensure cross-origin web content cannot trigger POST /load on the local admin API by default, for example by:

  • Enabling origin enforcement by default for unsafe methods, and/or
  • Requiring an unguessable token for /load (and other state-changing admin endpoints).

poc.zip
PR_DESCRIPTION.md

References

@mholt mholt published to caddyserver/caddy Feb 23, 2026
Published by the National Vulnerability Database Feb 24, 2026
Published to the GitHub Advisory Database Feb 24, 2026
Reviewed Feb 24, 2026
Last updated Feb 27, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(4th percentile)

Weaknesses

Cross-Site Request Forgery (CSRF)

The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor. Learn more on MITRE.

CVE ID

CVE-2026-27589

GHSA ID

GHSA-879p-475x-rqh2

Source code

Credits

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