Summary
Session fixation
Workarounds
Call Plug.Conn.configure_session(conn, renew: true) periodically and after privilege change. A custom authorization plug can be written where the create/3 method should return the conn only after Plug.Conn.configure_session/2 have been called on it.
References
https://github.com/danschultzer/pow/commit/578ffd3d8bb8e8a26077b644222186b108da474f
https://www.owasp.org/index.php/Session_fixation
Impact
The use of Plug.Session in Pow.Plug.Session is susceptible to session fixation attacks if a persistent session store is used for Plug.Session, such as Redis or a database. Cookie store, which is used in most Phoenix apps, doesn't have this vulnerability.
CVE-2020-5205 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low 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 (1.0.16); 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-2020-5205? CVE-2020-5205 is a medium-severity security vulnerability in pow (erlang), affecting versions < 1.0.16. It is fixed in 1.0.16.
- How severe is CVE-2020-5205? CVE-2020-5205 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 versions of pow are affected by CVE-2020-5205? pow (erlang) versions < 1.0.16 is affected.
- Is there a fix for CVE-2020-5205? Yes. CVE-2020-5205 is fixed in 1.0.16. Upgrade to this version or later.
- Is CVE-2020-5205 exploitable, and should I be worried? Whether CVE-2020-5205 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-2020-5205 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-2020-5205? Upgrade
powto 1.0.16 or later.