Summary
goshs has a Path Traversal issue
The multipart upload filename fix splits on the path separator but never rejects dot-dot, allowing a write outside the served tree.
Finding (Medium): upload filename escapes the served tree (residual of CVE-2026-35393)
The multipart filename fix (updown.go lines 135-136) splits on the path separator but never rejects "..". Uploading with filename=".." results in os.Create against the parent of the upload folder with a trailing marker character, outside the served tree, and the subsequent failed rename leaves that file behind. Verified: a file containing ESCAPED_WRITE_PROOF was written outside the webroot, unauthenticated, with the default configuration. Not claimed: a Windows-specific variant (Go's Part.FileName() already applies filepath.Base).
Suggested fixes
- Reject any upload filename that is "..", is empty after sanitisation, or resolves outside the upload folder; validate the final resolved destination rather than only transforming the input.
Tooling
AI assistance was used while investigating. The finding was reproduced against a running server on loopback.
Impact
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-2026-66063 has a CVSS score of 6.5 (Medium). 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 (2.1.5-0.20260727065949-f3ef599e4091); 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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goshs.de/goshs/v2 to 2.1.5-0.20260727065949-f3ef599e4091 or later; github.com/patrickhener/goshs/v2 to 2.1.5-0.20260727065949-f3ef599e4091 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-66063? CVE-2026-66063 is a medium-severity path traversal vulnerability in goshs.de/goshs/v2 (go), affecting versions <= 2.1.4. It is fixed in 2.1.5-0.20260727065949-f3ef599e4091. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-66063? CVE-2026-66063 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 packages are affected by CVE-2026-66063?
goshs.de/goshs/v2(go) (versions <= 2.1.4)github.com/patrickhener/goshs/v2(go) (versions <= 2.1.4)goshs.de/goshs(go) (versions <= 1.1.4)github.com/patrickhener/goshs(go) (versions <= 1.1.4)
- Is there a fix for CVE-2026-66063? Yes. CVE-2026-66063 is fixed in 2.1.5-0.20260727065949-f3ef599e4091. Upgrade to this version or later.
- Is CVE-2026-66063 exploitable, and should I be worried? Whether CVE-2026-66063 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-2026-66063 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-2026-66063?
- Upgrade
goshs.de/goshs/v2to 2.1.5-0.20260727065949-f3ef599e4091 or later - Upgrade
github.com/patrickhener/goshs/v2to 2.1.5-0.20260727065949-f3ef599e4091 or later
- Upgrade