Firefly III Webhook URL Validator IsValidWebhookUrl.php gethostbyname server-side request forgery

Summaryinfo

A vulnerability described as critical has been identified in Firefly III. This affects the function gethostbyname of the file IsValidWebhookUrl.php of the component Webhook URL Validator. Such manipulation leads to server-side request forgery. This vulnerability is traded as CVE-2026-71250. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Firefly III (unknown version). Affected by this issue is the function gethostbyname of the file IsValidWebhookUrl.php of the component Webhook URL Validator. The manipulation with an unknown input leads to a server-side request forgery vulnerability. Using CWE to declare the problem leads to CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Firefly III's webhook URL validator (IsValidWebhookUrl.php) filters most private/reserved IPv4 ranges but contains an explicit early-return that allows any resolved address in 127.0.0.0/8, permitting an authenticated user (with webhooks enabled, which is off by default) to configure a webhook targeting loopback services on the server. Additionally, the validator resolves the target hostname once via gethostbyname() at validation time, but the actual outbound request (StandardWebhookSender.php, via Guzzle) re-resolves the hostname independently at send time, allowing a DNS-rebinding attacker to pass validation against a public IP and have the real request delivered to a private or internal address. The webhook response body is only written to a server-side debug log, not returned to the triggering user, so this is a blind SSRF primitive rather than one with direct response read-back.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-71250 since 08/05/2026. The exploitation is known to be easy. The attack may be launched remotely. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 08/05/2026).

By approaching the search of inurl:IsValidWebhookUrl.php it is possible to find vulnerable targets with Google Hacking.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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• Firefly III

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