Summary
Mechanize sends credential headers to another origin after a meta refresh
mechanize applied no trust boundary to a meta refresh, so credentials set through Mechanize#request_headers= followed a refresh that pointed at another origin.
Details
Mechanize::HTTP::Agent#response_follow_meta_refresh fetched the refresh target with no notion of a crossed origin, so @request_headers were re-applied in full. An attacker who could place a meta refresh in a page the agent fetched, through stored content, an open redirect, or control of any page in the crawl, collected the same credentials as through an HTTP redirect, on a code path that had none of the redirect path's protections.
The refresh fetch passes an empty per-request headers hash, so only headers set through Mechanize#request_headers= were exposed.
This requires Mechanize#follow_meta_refresh = true. It is false by default, so an agent in its default configuration is not affected. Crawlers commonly enable it.
Workarounds
Leave Mechanize#follow_meta_refresh at its default of false, or avoid request_headers= for credentials when it is enabled.
Impact
An attacker who can place a meta refresh in any page the agent fetches captures bearer tokens and session cookies set through request_headers=. Disclosure only; no integrity or availability impact.
CVE-2026-107399 has a CVSS score of 6.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.14.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in mechanize v2.14.1. A meta refresh that points at another origin is now subject to the same rule as an HTTP redirect: credentials and cookies are withheld from the request that follows it.
Frequently Asked Questions
- What is CVE-2026-107399? CVE-2026-107399 is a medium-severity security vulnerability in mechanize (rubygems), affecting versions < 2.14.1. It is fixed in 2.14.1.
- How severe is CVE-2026-107399? CVE-2026-107399 has a CVSS score of 6.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mechanize are affected by CVE-2026-107399? mechanize (rubygems) versions < 2.14.1 is affected.
- Is there a fix for CVE-2026-107399? Yes. CVE-2026-107399 is fixed in 2.14.1. Upgrade to this version or later.
- Is CVE-2026-107399 exploitable, and should I be worried? Whether CVE-2026-107399 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-107399 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-107399? Upgrade
mechanizeto 2.14.1 or later.