CVE-2019-1020001

Path Traversal vulnerability that affects yard

Possible arbitrary path traversal and file access via yard server

Workarounds

For users who cannot upgrade, it is possible to perform path sanitization of HTTP requests at your webserver level. WEBrick, for example, can perform such sanitization by default (which you can use via yard server -s webrick), as can certain rules in your webserver configuration.

A path traversal vulnerability was discovered in YARD <= 0.9.19 when using yard server to serve documentation. This bug would allow unsanitized HTTP requests to access arbitrary files on the machine of a yard server host under certain conditions.

Thanks to CuongMX from Viettel Cyber Security for discovering this vulnerability.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2019-1020001 has a CVSS score of 7.5 (High). 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 (0.9.20); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Please upgrade to YARD v0.9.20 immediately if you are relying on yard server to host documentation in any untrusted environments.

1. What is CVE-2019-1020001? CVE-2019-1020001 is a high-severity path traversal vulnerability in yard (rubygems), affecting versions < 0.9.20. It is fixed in 0.9.20. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2019-1020001? CVE-2019-1020001 has a CVSS score of 7.5 (High). 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 yard are affected by CVE-2019-1020001? yard (rubygems) versions < 0.9.20 is affected.
4. Is there a fix for CVE-2019-1020001? Yes. CVE-2019-1020001 is fixed in 0.9.20. Upgrade to this version or later.
5. Is CVE-2019-1020001 exploitable, and should I be worried? Whether CVE-2019-1020001 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-2019-1020001 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-2019-1020001? Upgrade yard to 0.9.20 or later.

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