CVE-2026-69212 in Http4s
Summary
by MITRE • 09/15/2026
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, The FollowRedirect client middleware strips Authorization and Cookie headers only when a redirect changes authority, but authority comparison excludes the URI scheme. A same-authority redirect from HTTPS to HTTP therefore preserves credentials and transmits them over a plaintext connection. An attacker who can induce the downgrade and observe the network can capture those sensitive headers from applications using FollowRedirect. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in Http4s, a popular Scala interface for building HTTP services, represents a critical flaw in the implementation of its client-side redirect handling logic. Specifically, this issue resides within the FollowRedirect middleware component, which is responsible for automatically following HTTP redirection responses issued by servers. The core technical defect lies in how the middleware determines whether to strip sensitive headers such as Authorization and Cookie during a redirect operation. According to standard security practices, these credentials should be removed if the request moves from a secure context (HTTPS) to an insecure one (HTTP), or if it changes domains entirely, to prevent credential leakage over unencrypted channels. However, prior to versions 0.23.35 and 1.0.0-M47, the authority comparison logic used by Http4s failed to account for the URI scheme when evaluating whether a redirect constitutes a change in security context.
The technical flaw manifests because the middleware only strips Authorization and Cookie headers if it detects that the target URL's authority differs from the original request's authority. In Uniform Resource Identifier (URI) terminology, the authority typically comprises the host and port but excludes the scheme component such as http or https. Consequently, when a server issues a redirect response that changes the protocol from HTTPS to HTTP while keeping the same hostname and port number, Http4s incorrectly interprets this as a same-authority redirect. As a result, it preserves the sensitive headers and transmits them over the newly established plaintext connection. This behavior directly contradicts security best practices which dictate that credentials must never be sent over unencrypted connections if they were originally transmitted securely or are intended for secure contexts only.
From an operational impact perspective, this vulnerability enables a man-in-the-middle attack scenario where an adversary can induce protocol downgrades and subsequently capture sensitive authentication tokens and session cookies. An attacker positioned on the network path between the client application using Http4s and the target server could exploit this flaw by manipulating redirect responses or forcing SSL/TLS stripping attacks. Once the connection is downgraded to HTTP, the preserved Authorization header containing bearer tokens or basic auth credentials, along with Cookie headers maintaining user sessions, are transmitted in cleartext. This exposure allows attackers to hijack user accounts, escalate privileges, or access sensitive data protected by these authentication mechanisms. The impact is particularly severe for applications relying on Http4s for handling external API calls where redirect chains might involve mixed security contexts.
This vulnerability aligns with CWE-319, which classifies the use of cleartext transmission of sensitive information, and falls under MITRE ATT&CK technique T1557, specifically Adversary-in-the-Middle (AitM) scenarios involving credential interception. The failure to properly validate the security context change during redirects is a common pitfall in HTTP client implementations, often stemming from an overly narrow definition of what constitutes a domain or authority change. To mitigate this risk, developers must upgrade Http4s to version 0.23.35 or later for the 0.23.x branch and version 1.0.0-M47 or later for the main development line. These updated versions correct the authority comparison logic to include scheme validation, ensuring that redirects from HTTPS to HTTP trigger the appropriate stripping of sensitive headers. Additionally, organizations should enforce strict transport security policies such as HSTS on their servers to prevent protocol downgrades at the network level and implement Content Security Policy directives where applicable to further reduce the attack surface for credential interception attacks.