CVE-2026-107399 in Mechanize
Summary
by MITRE • 10/09/2026
The Mechanize library is used for automating interaction with websites. Prior to 2.14.1, Mechanize applies no origin trust boundary in Mechanize::HTTP::Agent#response_follow_meta_refresh when Mechanize#follow_meta_refresh is enabled. A page containing a meta refresh to another origin causes headers configured through Mechanize#request_headers= to be reapplied to the refresh request, allowing an attacker who controls content in the crawl to capture bearer tokens or session cookies. The default configuration is not affected because follow_meta_refresh is false, and the exposure is limited to caller-supplied default headers. This issue is fixed in version 2.14.1.
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Analysis
by VulDB Data Team • 10/09/2026
The Mechanize library serves as a critical tool for automating interactions with websites, particularly in web scraping and testing scenarios where maintaining session state or sending specific HTTP headers is required. A significant security flaw was identified within the Mechanize::HTTP::Agent#response_follow_meta_refresh method prior to version 2.14.1. This vulnerability stems from an absence of origin trust boundaries when handling meta refresh redirects, a common HTML mechanism used by websites to automatically redirect users to different URLs after a specified time interval or immediately upon page load. When the follow_meta_refresh configuration option is enabled, which allows Mechanize to automatically process these client-side redirects, the library fails to distinguish between same-origin and cross-origin requests regarding header propagation.
The core technical flaw involves the unconditional reapplication of headers configured via Mechanize#request_headers= to every subsequent request generated by a meta refresh, regardless of whether the target URL resides on the same origin as the initial page or a completely different domain. In standard web security models, browsers enforce strict policies that prevent cross-site requests from carrying sensitive credentials such as authentication tokens or session cookies unless explicitly permitted via CORS headers. Mechanize, operating at a lower level without these browser-enforced protections, blindly forwards any default request headers set by the application developer to the new destination. This behavior creates a severe information disclosure vector where an attacker who controls content within a crawled website can manipulate meta refresh tags to redirect requests to malicious infrastructure while retaining access to sensitive authorization data embedded in those headers.
The operational impact of this vulnerability is particularly acute for applications that rely on Mechanize to automate interactions with third-party services or user-generated content pages. If the default configuration includes bearer tokens, API keys, or session cookies in the request_headers array, these secrets are transmitted to arbitrary external domains upon encountering a crafted meta refresh tag. This allows an attacker to capture sensitive authentication material, potentially leading to unauthorized access to protected resources, account takeover, or further exploitation of downstream services that trust those credentials. The severity is compounded by the fact that many developers assume Mechanize behaves similarly to modern web browsers regarding security boundaries, not realizing that it acts as a transparent proxy for headers unless explicitly configured otherwise.
Mitigation strategies primarily involve upgrading to version 2.14.1 or later, where this logic has been corrected to respect origin boundaries and prevent the leakage of sensitive headers across domains. For environments unable to upgrade immediately, developers should ensure that follow_meta_refresh is set to false if meta refresh handling is not strictly required for their automation tasks. Additionally, it is crucial to audit any usage of Mechanize#request_headers= to avoid placing high-sensitivity credentials in default header configurations when interacting with untrusted or public-facing web content. This incident highlights the importance of applying strict origin validation and least-privilege principles even within automated client libraries that operate outside traditional browser security contexts, aligning with CWE-200 Information Exposure and ATT&CK techniques related to credential harvesting through intercepted network traffic.