Summary
Zio has SubFileSystem Path Confinement Bypass via Unresolved .. Segment
SubFileSystem fails to confine operations to its declared sub path when the input path is /../ (or equivalents /../, /..\\). This path passes all validation but resolves to the root of the parent filesystem, allowing directory level operations outside the intended boundary.
Affected Component
Zio.UPath.ValidateAndNormalizeZio.FileSystems.SubFileSystem
UPath.ValidateAndNormalize has a trailing slash optimisation.
if (!processParts && i + 1 == path.Length)
return path.Substring(0, path.Length - 1);
When the input ends with / or \, and processParts is still false, the function strips the trailing separator and returns immediately before the .. resolution logic runs. The input /../ triggers this path: the trailing / is the last character, processParts has not been set (because .. as the first relative segment after root is specifically exempted), so the function returns /.. with the .. segment unresolved.
The resulting UPath with FullName = "/.." is absolute, contains no control characters, and no colon so it passes FileSystem.ValidatePath without rejection.
When this path reaches SubFileSystem.ConvertPathToDelegate:
protected override UPath ConvertPathToDelegate(UPath path)
{
var safePath = path.ToRelative(); // "/..".ToRelative() = ".."
return SubPath / safePath; // "/jail" / ".." = "/" (resolved by Combine)
}
The delegate filesystem receives / (the root) instead of a path under /jail.
Proof of Concept
using Zio;
using Zio.FileSystems;
var root = new MemoryFileSystem();
root.CreateDirectory("/sandbox");
var sub = new SubFileSystem(root, "/sandbox");
Console.WriteLine(sub.DirectoryExists("/../")); // True (sees parent root)
Console.WriteLine(sub.ConvertPathToInternal("/../")); // "/" (parent root path)
Impact
The escape is limited to directory level operations because appending a filename after .. (e.g., /../file.txt) causes normal .. resolution to trigger, which correctly rejects the path as going above root. Only the bare terminal /../ (which strips to /..) survives. This means that exploitability is limited, and this vulnerability does not escalate to file read/write.
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.
GHSA-H39G-6X3C-7FQ9 has a CVSS score of 3.8 (Low). The vector is requires local access, 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 (0.22.2); 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 GHSA-H39G-6X3C-7FQ9? GHSA-H39G-6X3C-7FQ9 is a low-severity path traversal vulnerability in Zio (nuget), affecting versions <= 0.22.1. It is fixed in 0.22.2. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is GHSA-H39G-6X3C-7FQ9? GHSA-H39G-6X3C-7FQ9 has a CVSS score of 3.8 (Low). 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 Zio are affected by GHSA-H39G-6X3C-7FQ9? Zio (nuget) versions <= 0.22.1 is affected.
- Is there a fix for GHSA-H39G-6X3C-7FQ9? Yes. GHSA-H39G-6X3C-7FQ9 is fixed in 0.22.2. Upgrade to this version or later.
- Is GHSA-H39G-6X3C-7FQ9 exploitable, and should I be worried? Whether GHSA-H39G-6X3C-7FQ9 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 GHSA-H39G-6X3C-7FQ9 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 GHSA-H39G-6X3C-7FQ9? Upgrade
Zioto 0.22.2 or later.