CVE-2026-76239 in Stigmem
Summary
by MITRE • 08/19/2026
Stigmem before 0.9.0a11 fails to validate the delivery_address parameter when creating webhook subscriptions, allowing authenticated users to specify internal loopback and private network destinations. Attackers can trigger matching fact-change events to cause the Stigmem server to issue server-side HTTP POST requests to internal services, enabling blind SSRF attacks against localhost and private network endpoints.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in Stigmem versions prior to 0.9.0a11 represents a critical Server-Side Request Forgery (SSRF) flaw rooted in insufficient input validation within the webhook subscription management functionality. When an authenticated user creates or modifies a webhook subscription, the application accepts a delivery_address parameter intended to specify where HTTP POST requests should be sent upon triggering events such as fact changes. The core technical failure lies in the absence of rigorous sanitization and domain verification logic for this parameter. Specifically, the system fails to reject URLs that resolve to internal loopback addresses like 127.0.0.1 or localhost, as well as those targeting private network ranges defined by RFC 1918, such as 10.x.x.x, 172.16-31.x.x, and 192.168.x.x. This oversight allows an attacker to manipulate the destination of server-initiated traffic, effectively turning the Stigmem application into a proxy for internal network reconnaissance or exploitation of services that are not directly exposed to the public internet.
From an operational perspective, this vulnerability enables blind SSRF attacks against localhost and private network endpoints. Because webhook deliveries often occur asynchronously in response to specific triggers like fact-change events, an attacker can induce these requests by manipulating data within the Stigmem environment to match their configured conditions. The server then issues HTTP POST requests to the maliciously specified internal addresses without returning immediate feedback to the user regarding the success or failure of the request. This blind nature complicates detection and exploitation but does not diminish its severity, as it can be leveraged for port scanning, service fingerprinting, or exploiting vulnerabilities in backend services such as databases, administrative panels, or microservices that reside within the same network segment. The ability to reach localhost is particularly dangerous as many internal applications bind exclusively to 127.0.0.1 under the assumption they are protected from external access, a security boundary this vulnerability effectively bypasses through server-side execution context.
This flaw aligns with CWE-918, which describes Server-Side Request Forgery (SSRF) flaws where web applications retrieve data from remote servers without validating user-supplied URLs. Furthermore, the exploitation technique maps to MITRE ATT&CK tactic T1046, Network Service Discovery, and potentially T1572, Protocol Tunneling, depending on how the attacker utilizes the forged requests to interact with internal protocols or exfiltrate data through covert channels. The vulnerability underscores a common misconfiguration pattern where authentication is present but input validation for network-facing parameters remains lax, assuming that authenticated users are trusted entities capable of safe configuration changes.
To mitigate this risk, immediate remediation requires upgrading Stigmem to version 0.9.0a11 or later, which implements proper validation logic for the delivery_address parameter. In cases where an upgrade is not immediately feasible, defensive measures should include implementing a strict allowlist for webhook destinations that restricts URLs to known external domains and explicitly blocks private IP ranges and loopback addresses at the application level. Additionally, deploying network-level controls such as egress filtering on the Stigmem server can prevent outbound connections to internal subnets or localhost, adding a layer of defense-in-depth. Security teams should also audit existing webhook configurations for any suspicious entries that may have been injected prior to patching and monitor logs for unusual outbound HTTP POST requests originating from the application process.