CVE-2026-56708 in API Plugin
Summary
by MITRE • 08/25/2026
Grav API plugin before 1.0.16 contains a server-side request forgery vulnerability in webhook delivery that allows attackers to bypass hostname validation by DNS rebinding. Attackers controlling authoritative DNS for a configured webhook hostname can answer validation lookups with public addresses and delivery lookups with private addresses to reach internal network resources.
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Analysis
by VulDB Data Team • 08/25/2026
The Grav API plugin, prior to version 1.0.16, contains a critical server-side request forgery vulnerability within its webhook delivery mechanism that exploits weaknesses in hostname validation logic. This flaw allows an attacker who controls the authoritative DNS records for a configured webhook hostname to manipulate the resolution process during different stages of the HTTP request lifecycle. By leveraging DNS rebinding techniques, the attacker can serve public IP addresses when the application performs initial security checks or host verification steps, thereby passing these validations successfully. However, once the actual connection is established and data delivery begins, the same hostname resolves to private internal network addresses. This discrepancy enables the attacker to bypass perimeter defenses and initiate requests directly against internal services that are not exposed to the public internet, effectively turning the webhook feature into a proxy for accessing restricted resources within the local network infrastructure.
This vulnerability aligns with Common Weakness Enumeration CWE-918, which describes Server-Side Request Forgery (SSRF), specifically highlighting flaws in server-side URL parsing and hostname validation. The attack vector relies on the application's failure to maintain consistent DNS resolution context or enforce strict allow-listing of IP addresses after initial host verification. In many web frameworks, including those used by Grav, developers may validate that a provided domain resolves to an expected public range before proceeding with outbound requests. However, if this validation is performed only once at the beginning of the request handling process without re-validating during the actual network connection phase, DNS rebinding becomes viable. The attacker exploits the time gap between the initial check and the final socket creation by changing the DNS records in real-time or using TTL manipulation to switch from a public IP to a private RFC 1918 address such as those in the 10.x.x.x, 172.16.x.x-172.31.x.x, or 192.168.x.x ranges.
From an operational perspective, this vulnerability poses significant risks to organizations that rely on webhook integrations for automated workflows, notifications, or third-party service interactions. Successful exploitation can lead to unauthorized access to internal APIs, database servers, management interfaces, or other sensitive services residing behind firewalls and network segmentation controls. Attackers could potentially exfiltrate data from these internal systems, disrupt business operations by sending malicious payloads to critical infrastructure components, or use the compromised server as a pivot point for further lateral movement within the enterprise network. The impact is particularly severe in environments where webhook endpoints are configured with high privileges or when they interact with services that lack additional authentication mechanisms on their local interfaces.
To mitigate this vulnerability, organizations must upgrade the Grav API plugin to version 1.0.16 or later, which addresses the hostname validation logic to prevent DNS rebinding attacks. In addition to updating software, administrators should implement defense-in-depth strategies such as enforcing strict IP allow-listing for outbound connections rather than relying solely on domain name verification. Network-level controls like egress filtering can also be employed to restrict outbound traffic from web servers to only known and necessary destinations, thereby blocking requests directed at private address ranges regardless of how the hostname was resolved. Furthermore, it is advisable to isolate webhook processing services in dedicated network segments with limited access to internal resources, ensuring that even if a vulnerability like SSRF is exploited, the blast radius remains contained. Security teams should also monitor outbound traffic for anomalies indicative of DNS rebinding attempts and ensure that all third-party plugins are regularly audited for similar validation flaws.