Summary
HTTP Request Smuggling in hyper
Vulnerable versions of hyper allow GET requests to have bodies, even if there is no Transfer-Encoding or Content-Length header. As per the HTTP 1.1 specification, such requests do not have bodies, so the body will be interpreted as a separate HTTP request.
This allows an attacker who can control the body and method of an HTTP request made by hyper to inject a request with headers that would not otherwise be allowed, as demonstrated by sending a malformed HTTP request from a Substrate runtime. This allows bypassing CORS restrictions. In combination with other vulnerabilities, such as an exploitable web server listening on loopback, it may allow remote code execution.
The flaw was corrected in hyper version 0.12.34.
Impact
CVE-2020-35863 has a CVSS score of 9.8 (Critical). 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 (0.12.34); 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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Frequently Asked Questions
- What is CVE-2020-35863? CVE-2020-35863 is a critical-severity security vulnerability in hyper (rust), affecting versions >= 0.11.0, < 0.12.34. It is fixed in 0.12.34.
- How severe is CVE-2020-35863? CVE-2020-35863 has a CVSS score of 9.8 (Critical). 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 hyper are affected by CVE-2020-35863? hyper (rust) versions >= 0.11.0, < 0.12.34 is affected.
- Is there a fix for CVE-2020-35863? Yes. CVE-2020-35863 is fixed in 0.12.34. Upgrade to this version or later.
- Is CVE-2020-35863 exploitable, and should I be worried? Whether CVE-2020-35863 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-2020-35863 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-2020-35863? Upgrade
hyperto 0.12.34 or later.