CVE-2019-19703 in Ktor
Summary
by MITRE
In Ktor through 1.2.6, the client resends data from the HTTP Authorization header to a redirect location.
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Analysis
by VulDB Data Team • 03/10/2024
The vulnerability identified as CVE-2019-19703 affects the Ktor HTTP client library version 1.2.6 and earlier, presenting a security risk through improper handling of HTTP redirects. This flaw specifically manifests when the client encounters a redirect response and automatically resends the original request including the Authorization header to the new location. The issue stems from the client's default behavior of forwarding authentication credentials without proper validation or consideration of the target endpoint's security context. This vulnerability falls under the category of information disclosure through credential exposure, as sensitive authentication data may be transmitted to unintended recipients during the redirect process.
The technical implementation of this vulnerability involves the HTTP client's redirect handling mechanism which operates without sufficient security checks. When a request is made to a server that responds with a redirect status code such as 301, 302, or 307, the Ktor client automatically follows the redirect and includes the original Authorization header in the subsequent request. This behavior is problematic because the original request may have been authenticated against a specific resource or service, but the redirect target could be a completely different server or domain. The flaw represents a violation of the principle of least privilege and demonstrates inadequate security controls in the client-side redirect processing logic.
From an operational impact perspective, this vulnerability creates significant risks for applications that rely on Ktor for HTTP communications and implement authentication mechanisms. Attackers who can influence or intercept redirect paths may gain access to authentication tokens, session identifiers, or other sensitive credential information that would normally be restricted to the original server. The vulnerability can be exploited in scenarios involving man-in-the-middle attacks, where an attacker controls or can monitor the redirect destination and captures the transmitted credentials. This exposure could lead to unauthorized access to protected resources, privilege escalation, and potential data breaches. The impact is particularly severe in environments where the redirect target is not under the organization's direct control or where the redirect destination is a third-party service.
Mitigation strategies for CVE-2019-19703 should focus on both immediate code-level fixes and architectural considerations. The most direct approach involves updating to Ktor version 1.2.7 or later, where the redirect handling behavior has been corrected to prevent automatic resending of authorization headers. Organizations should also implement proper redirect validation mechanisms that verify the security context of redirect destinations before forwarding authentication credentials. This includes configuring the client to either disable automatic redirects entirely or to implement explicit redirect handling that evaluates whether credentials should be forwarded based on domain matching or security policies. The vulnerability aligns with CWE-200, Information Exposure, and can be mapped to ATT&CK technique T1566 for credential access through social engineering or network manipulation, and T1071 for application layer protocol usage. Security teams should also consider implementing network monitoring to detect unusual redirect patterns and credential forwarding behaviors that may indicate exploitation attempts.