Summary
phoenix_html allows Cross-site Scripting in HEEx class attributes
tag.ex in Phoenix Phoenix.HTML (aka phoenix_html) before 3.0.4 allows XSS in HEEx class attributes
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2021-46871 has a CVSS score of 6.1 (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 (3.0.4); 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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phoenix_html to 3.0.4 or later; phoenix_html to 3.0.4 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-46871? CVE-2021-46871 is a medium-severity cross-site scripting (XSS) vulnerability in phoenix_html (npm), affecting versions < 3.0.4. It is fixed in 3.0.4. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2021-46871? CVE-2021-46871 has a CVSS score of 6.1 (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 phoenix_html are affected by CVE-2021-46871? phoenix_html (npm) versions < 3.0.4 is affected.
- Is there a fix for CVE-2021-46871? Yes. CVE-2021-46871 is fixed in 3.0.4. Upgrade to this version or later.
- Is CVE-2021-46871 exploitable, and should I be worried? Whether CVE-2021-46871 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-2021-46871 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-2021-46871?
- Upgrade
phoenix_htmlto 3.0.4 or later - Upgrade
phoenix_htmlto 3.0.4 or later
- Upgrade