Summary
HTTP request smuggling in netty
Impact
Netty currently just skips control chars when these are present at the beginning / end of the header name. We should better fail fast as these are not allowed by the spec and could lead to HTTP request smuggling.
Failing to do the validation might cause netty to "sanitize" header names before it forward these to another remote system when used as proxy. This remote system can't see the invalid usage anymore and so not do the validation itself.
CVE-2021-43797 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (4.1.71.Final); 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.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-43797? CVE-2021-43797 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.0.0, < 4.1.71.Final. It is fixed in 4.1.71.Final.
- How severe is CVE-2021-43797? CVE-2021-43797 has a CVSS score of 6.5 (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 packages are affected by CVE-2021-43797?
io.netty:netty-codec-http(maven) (versions >= 4.0.0, < 4.1.71.Final)org.jboss.netty:netty(maven) (versions < 4.0.0)io.netty:netty(maven) (versions < 4.0.0)
- Is there a fix for CVE-2021-43797? Yes. CVE-2021-43797 is fixed in 4.1.71.Final. Upgrade to this version or later.
- Is CVE-2021-43797 exploitable, and should I be worried? Whether CVE-2021-43797 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-2021-43797 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-2021-43797? Upgrade
io.netty:netty-codec-httpto 4.1.71.Final or later.