CVE-2026-42091: goshs has Cross-Origin Arbitrary File Write via Missing CSRF on PUT and Wildcard CORS

Vulnerability summary

CVE-2026-42091 is a medium (CVSS 6.5) Cross-Site Request Forgery (CSRF) vulnerability in goshs. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 12.5% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 04-05-2026
   PublishedVulnerability first disclosed.
2. 05-05-2026
   Last modifiedVulnerability information updated.

Description

goshs is a SimpleHTTPServer written in Go. Prior to version 2.0.2, the PUT upload handler (httpserver/updown.go) lacks the CSRF token validation that was added to the POST upload handler during the CVE-2026-40883 fix. Combined with the unconditional Access-Control-Allow-Origin: * on the OPTIONS preflight handler (httpserver/server.go), any website can write arbitrary files to a goshs instance through the victim's browser — bypassing network isolation (e.g. localhost, internal network). This issue has been patched in version 2.0.2.

• CWE-352Cross-Site Request Forgery (CSRF)The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.