Description

An unrecovered panic in the event stream header decoder in Amazon AWS SDK for Go v2 before release-2026-03-23 might allow an unauthenticated remote actor to terminate the consuming application process via a crafted event stream response frame containing a header value type outside the valid range. To remediate this issue, users should upgrade to release-2026-03-23 or later, and patch any forked or derivative code.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.9",
  "pubDate": "2026-09-11T18:17:00.097Z",
  "pubdate": "2026-09-11T18:17:00.097Z",
  "executiveSummary": "A critical vulnerability exists in the Amazon AWS SDK for Go v2, specifically within the event stream header decoder, prior to the release-2026-03-23 update.\nThe vulnerability is characterized as an unrecovered panic triggered by improperly validated input, which allows an unauthenticated remote actor to force a Denial of Service (DoS) by crashing the consuming application process.\nThe flaw occurs when the decoder processes a malicious event stream response frame containing a header value type that falls outside the defined range of acceptable values.\nBecause the SDK fails to handle these erroneous inputs gracefully, the process terminates immediately upon encounter.\nThis represents a significant availability risk for services relying on the AWS SDK for Go, as no specialized privileges or authentication are required to trigger the crash; an attacker merely needs the ability to influence the event stream data interpreted by the client.\nImpact is limited to application unavailability, but given the critical nature of AWS SDK integrations, this could result in widespread service disruption.",
  "technicalDetails": "The vulnerability resides in the event stream header parsing logic within the Amazon AWS SDK for Go v2. The root cause is an insufficient validation of header value types during the frame decoding process.\nEvent stream protocols often utilize a tagged-type system for header metadata. When the decoder encounters a header frame, it performs a look-up or type-switch operation to cast the raw byte stream into a structured Go type based on the provided type identifier.\nThe vulnerability exists because the decoder implementation fails to include an exhaustive default case or comprehensive bounds checking when processing these type identifiers. When a crafted frame is supplied with a type identifier that exists outside of the expected enumeration range, the Go runtime triggers a panic.\nIn the context of the AWS SDK for Go, this panic remains unrecovered within the decoder stack, propagating upwards until it reaches the application runtime, resulting in an abrupt process termination.\nThe attack flow proceeds as follows: An attacker with the ability to influence the response stream—either through a compromised upstream service, a Man-in-the-Middle (MitM) position, or by simulating an AWS service response—crafts a specific binary payload. This payload is structured as an event stream frame with a header containing an invalid or undefined type identifier.\nUpon receipt, the SDK's header decoder attempts to map this identifier to a handler. Finding no match or encountering an out-of-bounds index, the internal state machine hits an execution path not guarded by error handling or recovery blocks (e.g., defer/recover).\nBecause the vulnerability exists in the core communication logic, no authentication or specific authorization is required from the attacker to initiate the crash, as the payload is processed during the routine handling of event streams.\nThis exploit is highly effective for an attacker aiming to disrupt operational services, as it bypasses application-level logic by crashing the underlying networking infrastructure of the SDK itself, leading to complete service interruption for the consuming client process.\nThe vulnerable component is the event stream header decoding module within versions prior to release-2026-03-23."
}