Summary
Decidim: Push subscriptions can be abused for server-side requests
Description
The push-subscription endpoint stores an attacker-controlled delivery URL, and the notification send path becomes an outbound-request sink when VAPID delivery is enabled. The practical result is an authenticated, stored, mostly blind SSRF primitive to arbitrary HTTPS endpoints reachable from the app server.
Technical description
When VAPID delivery is enabled, the notification subscription flow stores the client-supplied push endpoint without checking that it belongs to an approved push service. The send path later passes that stored URL to WebPush.payload_send, turning the subscription into an attacker-controlled outbound request destination.
This is the source-to-sink chain:
- Source: attacker-controlled
subscription.endpointin the JSON body posted toPOST /notifications_subscriptions. - Persistence:
params[:endpoint]is stored underuser.notification_settings["subscriptions"]. - Retrieval:
user.notifications_subscriptions.valuesreturns that stored endpoint later. - Sink:
build_payloadsetsendpoint: subscription["endpoint"]. - Outbound request:
WebPush.payload_send(**payload)uses the attacker-supplied endpoint as the
destination.
One spec asserts that the endpoint is persisted exactly as supplied:
# decidim-core/spec/services/decidim/notifications_subscriptions_persistor_spec.rb
expect(user.notifications_subscriptions["auth_code_121"]["endpoint"]).to eq(params[:endpoint])
Another spec asserts that SendPushNotification passes the stored endpoint into WebPush.payload_send:
# decidim-core/spec/services/decidim/send_push_notification_spec.rb
first_notification_payload = {
message:,
endpoint: subscriptions["auth_key_1"]["endpoint"],
p256dh: subscriptions["auth_key_1"]["p256dh"],
auth: subscriptions["auth_key_1"]["auth"],
vapid: a_hash_including(...)
}
expect(WebPush).to receive(:payload_send).with(first_notification_payload)
Workarounds
Disable the push notifications feature by removing the VAPID keys in the server.
Resource
SSRF
Credits
This issue was discovered in a security audit organized by the Decidim Association and made by Radically Open Security against Decidim financed by NGI.
Impact
- In a configured deployment, an authenticated user can register an attacker-controlled or otherwise unauthorized HTTPS URL.
- The server then sends outbound
POSTrequests there whenever a notification is pushed. - This is a stored, mostly blind SSRF primitive: useful for outbound interaction with attacker infrastructure and, where routable, internal HTTPS services.
- Notification metadata is disclosed to the supplied endpoint through the encrypted web push request path.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-45573 has a CVSS score of 6.4 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.30.9, 0.31.5, 0.32.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Frequently Asked Questions
- What is CVE-2026-45573? CVE-2026-45573 is a medium-severity server-side request forgery (SSRF) vulnerability in decidim-core (rubygems), affecting versions < 0.30.9. It is fixed in 0.30.9, 0.31.5, 0.32.0. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-45573? CVE-2026-45573 has a CVSS score of 6.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of decidim-core are affected by CVE-2026-45573? decidim-core (rubygems) versions < 0.30.9 is affected.
- Is there a fix for CVE-2026-45573? Yes. CVE-2026-45573 is fixed in 0.30.9, 0.31.5, 0.32.0. Upgrade to this version or later.
- Is CVE-2026-45573 exploitable, and should I be worried? Whether CVE-2026-45573 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45573 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45573?
- Upgrade
decidim-coreto 0.30.9 or later - Upgrade
decidim-coreto 0.31.5 or later - Upgrade
decidim-coreto 0.32.0 or later
- Upgrade