CVE-2026-61681 in Hatchet
Summary
by MITRE • 09/21/2026
Hatchet is a platform for orchestrating background tasks, AI agents, and durable workflows at scale. Prior to 0.91.1, the SNS UnsubscribeConfirmation handler in internal/integrations/ingestors/sns/sns.go calls http.Get() on payload.UnsubscribeURL after VerifyPayload() even though BuildSignature() excludes UnsubscribeURL, allowing an authenticated Hatchet tenant to replace that field in an otherwise valid AWS-signed message with an internal URL. The server-side request can reach EC2 Instance Metadata Service, internal services, and internal HTTP APIs, potentially exposing IAM credentials or network-accessible data and functionality. This issue is fixed in version 0.91.1.
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Analysis
by VulDB Data Team • 09/21/2026
The vulnerability identified within the Hatchet platform prior to version 0.91.1 represents a critical Server-Side Request Forgery (SSRF) flaw rooted in an inconsistency between signature verification and payload validation logic. Hatchet serves as a system for orchestrating background tasks, AI agents, and durable workflows at scale, relying heavily on secure integration with external services such as Amazon Simple Notification Service (SNS). The specific defect resides in the SNS UnsubscribeConfirmation handler located within the internal ingestors module. When processing an unsubscribe confirmation message from AWS, the application first verifies the cryptographic signature of the incoming payload to ensure its authenticity and integrity. However, a logical error exists wherein the function responsible for building or validating the signature does not include the UnsubscribeURL field in the data set used for hashing. This omission creates a significant security gap where an attacker who possesses valid authentication credentials for a Hatchet tenant can manipulate the message content without invalidating the digital signature.
By exploiting this discrepancy, an authenticated user can replace the legitimate AWS unsubscribe URL with a maliciously crafted internal address while keeping the original cryptographic signature intact. Because the server trusts the payload based on the verified signature but fails to validate that the UnsubscribeURL was part of that signed data set, it proceeds to execute an HTTP GET request against the attacker-controlled target. This behavior allows the application server to act as a proxy for arbitrary network requests initiated by authenticated users. The operational impact is severe because the SSRF capability enables access to sensitive internal resources that are typically isolated from external networks. Specifically, attackers can direct these forged requests toward the EC2 Instance Metadata Service (IMDS), which hosts critical IAM role credentials and other instance-specific configuration data. Accessing IMDS allows an attacker to retrieve temporary security credentials, potentially leading to full compromise of the underlying infrastructure if those roles have excessive permissions.
Beyond credential theft, this vulnerability facilitates broader network reconnaissance and exploitation within the internal environment. The forged requests can target internal HTTP APIs, microservices, or other backend systems that are not exposed to the public internet but are accessible from the Hatchet deployment's network segment. This exposure could lead to unauthorized data exfiltration, manipulation of internal service states, or further pivoting into more critical parts of the infrastructure. The flaw is classified under CWE-918, which addresses Server-Side Request Forgery (SSRF) flaws where a web server makes requests based on user-supplied input without proper validation. In terms of offensive security frameworks, this vulnerability aligns with MITRE ATT&CK technique T1557, specifically Adversary-in-the-Middle or Lateral Tool Transfer scenarios involving SSRF to access internal resources. It also relates to CWE-20, Improper Input Validation, as the application fails to ensure that all mutable fields in a signed payload are included in the signature verification process.
To mitigate this vulnerability and prevent similar issues in future development cycles, it is imperative to enforce strict validation of all user-controllable or externally-supplied data before processing. The primary fix involves ensuring that the BuildSignature function includes every field from the payload that will be used operationally after verification, thereby binding the UnsubscribeURL to the cryptographic signature. This ensures that any modification to the URL by an attacker would result in a signature mismatch and subsequent rejection of the request. Additionally, implementing network-level controls such as egress filtering can provide defense-in-depth by restricting outbound HTTP requests from application servers to only known external endpoints or internal services explicitly required for business logic. For organizations using Hatchet versions prior to 0.91.1, immediate upgrading is recommended to resolve this critical security defect and restore the integrity of the SNS integration workflow.