CVE-2026-103030 in dio
Summary
by MITRE • 10/13/2026
Dio is a powerful HTTP client for Dart and Flutter. From 1.0.0 until 2.8.0, dio_http2_adapter follows redirects in Http2Adapter._fetch by copying the original RequestOptions.headers into the redirected HTTP/2 request without comparing the source and destination origins. A server contacted by an application can return a cross-origin Location redirect to a different-origin destination, which then receives preserved Authorization, Cookie, and Proxy-Authorization headers because RequestOptions.copyWith retains the full header map. The issue applies when applications use Http2Adapter for authenticated requests, and redirect following is enabled by default. This issue is fixed in version 2.8.0.
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Analysis
by VulDB Data Team • 10/13/2026
The Dio library serves as a robust HTTP client solution widely adopted within Dart and Flutter ecosystems for managing network communications. A significant security vulnerability was identified in the dio_http2_adapter package, specifically affecting versions ranging from 1.0.0 through 2.8.0. This flaw resides within the Http2Adapter._fetch method, which is responsible for handling HTTP/2 connections and following redirects. The core technical deficiency involves the improper handling of request headers during redirect operations. When a server responds with an HTTP status code indicating a redirection, such as 301 or 302, along with a Location header pointing to a different URI, the adapter automatically follows this redirect without performing any origin validation checks.
The mechanism behind this vulnerability lies in how the library constructs subsequent requests after receiving a redirect response. Instead of sanitizing or filtering headers based on the new destination's security context, the implementation copies the original RequestOptions.headers directly into the redirected HTTP/2 request. This behavior is driven by the copyWith method within the RequestOptions class, which retains the complete header map from the initial request. Consequently, sensitive authentication credentials and session tokens are blindly transmitted to potentially untrusted or cross-origin destinations. This lack of origin comparison means that if an attacker can manipulate a redirect chain, they can force the client to send confidential data to a malicious server under their control.
The operational impact of this vulnerability is severe for applications relying on authenticated HTTP/2 connections with default redirect following enabled. Attackers who possess the ability to intercept or modify network traffic, such as through man-in-the-middle attacks or by compromising an intermediate proxy, can exploit this flaw. By injecting a cross-origin Location header into a response, they can trick the application into sending Authorization headers containing bearer tokens, Cookie headers with session identifiers, and Proxy-Authorization headers to a malicious endpoint. This leads directly to credential theft and potential account takeover, as the attacker gains access to active sessions or valid authentication credentials intended for legitimate services.
This vulnerability aligns closely with CWE-200, which covers Exposure of Sensitive Information to an Unauthorized Actor, specifically within the context of improper redirect handling that leaks sensitive headers across origin boundaries. From a tactical perspective, this behavior mirrors techniques found in the MITRE ATT&CK framework under T1539, Steal Web Session Cookie, and potentially contributes to broader credential harvesting strategies by bypassing standard browser-like security models that typically strip credentials on cross-origin redirects. The failure to implement strict same-origin policy enforcement for HTTP/2 requests represents a critical deviation from secure coding practices expected in modern web clients.
To mitigate this risk, developers must upgrade the dio_http2_adapter package to version 2.8.0 or later, where the issue has been resolved by implementing proper origin checks before forwarding headers during redirects. For applications unable to immediately update dependencies, it is advisable to disable automatic redirect following and manually handle redirection logic with explicit security validations. This includes verifying that the destination URL shares the same scheme, host, and port as the original request before appending sensitive headers such as Authorization or Cookie. Additionally, implementing strict Content Security Policy directives and monitoring for unusual outbound traffic patterns can provide supplementary layers of defense against exploitation attempts targeting this specific header leakage vector.