CVE-2019-16782

There's a possible information leak / session hijack vulnerability in Rack. Attackers may be able to find and hijack sessions by using timing attacks targeting the session id. Session ids are usually stored and indexed in a database that uses some kind of scheme for speeding up lookups of that session id. By carefully measuring the amount of time it takes to look up a session, an attacker may be able to find a valid session id and hijack the session.

The session id itself may be generated randomly, but the way the session is indexed by the backing store does not use a secure comparison.

Releases

The 1.6.12 and 2.0.8 releases are available at the normal locations.

Workarounds

There are no known workarounds.

Credits

Thanks Will Leinweber for reporting this!

The session id stored in a cookie is the same id that is used when querying the backing session storage engine. Most storage mechanisms (for example a database) use some sort of indexing in order to speed up the lookup of that id. By carefully timing requests and session lookup failures, an attacker may be able to perform a timing attack to determine an existing session id and hijack that session.

CVE-2019-16782 has a CVSS score of 6.3 (Medium). The vector is network-reachable, low 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 (1.6.12, 2.0.8); upgrading removes the vulnerable code path.

Kodem intelligence

To aid users who aren't able to upgrade immediately we have provided patches for
the two supported release series. They are in git-am format and consist of a
single changeset.

• 1-6-session-timing-attack.patch - Patch for 1.6 series
• 2-0-session-timing-attack.patch - Patch for 2.6 series

1. What is CVE-2019-16782? CVE-2019-16782 is a medium-severity security vulnerability in rack (rubygems), affecting versions < 1.6.12. It is fixed in 1.6.12, 2.0.8.
2. How severe is CVE-2019-16782? CVE-2019-16782 has a CVSS score of 6.3 (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.
3. Which versions of rack are affected by CVE-2019-16782? rack (rubygems) versions < 1.6.12 is affected.
4. Is there a fix for CVE-2019-16782? Yes. CVE-2019-16782 is fixed in 1.6.12, 2.0.8. Upgrade to this version or later.
5. Is CVE-2019-16782 exploitable, and should I be worried? Whether CVE-2019-16782 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
6. What actually determines whether CVE-2019-16782 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.
7. How do I fix CVE-2019-16782?
   • Upgrade rack to 1.6.12 or later
   • Upgrade rack to 2.0.8 or later