CVE-2026-91080 in webhook
Summary
by MITRE • 09/14/2026
webhook through 2.8.3 reads the entire request body into memory before evaluating trigger rules, allowing unauthenticated attackers to exhaust memory by sending oversized bodies. Attackers can send multi-gigabyte request bodies with invalid signatures to trigger out-of-memory conditions and crash the service.
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in webhook implementations prior to version 2.8.3 represents a critical resource exhaustion flaw stemming from improper input validation and memory management practices during HTTP request processing. Specifically, the system is designed to ingest the entire body of an incoming webhook payload into volatile random-access memory before performing any security checks or trigger rule evaluations. This architectural decision creates a significant attack surface for unauthenticated adversaries who can exploit this behavior by transmitting excessively large data payloads with invalid authentication signatures. Because the validation logic occurs after the full ingestion, the system fails to implement size limits or streaming mechanisms that would typically prevent such abuse, leaving the service vulnerable to denial-of-service conditions driven by memory depletion rather than CPU exhaustion.
From a technical perspective, this flaw aligns closely with CWE-400, which describes uncontrolled resource consumption, and more specifically CWE-789, regarding the allocation of resources without limits or thresholds. The operational impact is severe for any service relying on these webhooks to process external events, as an attacker can trigger out-of-memory errors by sending multi-gigabyte request bodies that exceed available heap space. This results in the immediate crash or unresponsiveness of the webhook handler service, effectively causing a denial of service for legitimate users and potentially destabilizing the underlying host system if memory limits are not strictly enforced at the operating system level. The attack vector is straightforward and does not require authentication, making it easily exploitable by automated tools across the internet.
In terms of threat modeling, this vulnerability can be mapped to MITRE ATT&CK technique T1498, specifically Network Denial of Service via resource exhaustion. Adversaries leverage this weakness to disrupt availability without needing valid credentials or complex exploitation chains. The simplicity of sending a large POST request with an invalid signature makes it difficult for basic rate-limiting controls to mitigate the impact once the payload is received and buffered by the application layer.
To remediate this issue, developers must upgrade to version 2.8.3 or later where the processing logic has been corrected to evaluate trigger rules and validate signatures before fully loading the request body into memory. For systems that cannot be immediately upgraded, implementing a reverse proxy such as Nginx with strict client_max_body_size directives can help reject oversized requests at the network edge before they reach the application server. Additionally, configuring stream processing or chunked transfer encoding support within the webhook handler ensures that data is processed incrementally rather than buffered entirely in RAM. Enforcing strict content-length headers and implementing early validation of authentication tokens against small metadata fragments can also provide a layer of defense-in-depth to prevent resource exhaustion attacks.