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CVE-2026-27589 — v2

Fix: caddyserver/caddy@65e0ddc

CVE-2026-27589 is a Cross-Site Request Forgery (CSRF) vulnerability in github.com/caddyserver/caddy/v2. A fix is available for github.com/caddyserver/caddy/v2 — see the affected versions and patch details below.

Caddy vulnerable to cross-origin config application via local admin API /load (caddy)

Also known asGHSA-879p-475x-rqh2GO-2026-4537
Published
Feb 24, 2026
Updated
Aug 12, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Sep 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27589.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs6th percentile — riskier than 6% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected
🐹github.com/caddyserver/caddy/v2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

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

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/caddyserver/caddy/v2all versions2.11.1go get github.com/caddyserver/caddy/v2@v2.11.1

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/caddyserver/caddy/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/caddyserver/caddy/v2 to 2.11.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27589 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27589 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-27589. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 wi
O3 Security · Impact-Aware SCA

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O3 Security finds CVE-2026-27589 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

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CVE-2026-27589: v2 | O3 Security