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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

4 May 2026 17:24:47 UTC

Source modified

5 May 2026 14:14:46 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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.

Source published

May 4, 2026, 5:24:47 PM (timezone not stated)

Source modified

May 5, 2026, 2:14:46 PM (timezone not stated)

Observed here

7 Nov 2026 09:32:09 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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.

Source published

4 May 2026 18:16:31 UTC

Source modified

26 Oct 2026 19:10:00 UTC

Observed here

27 Oct 2026 11:12:01 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

### Summary The PUT upload handler (`httpserver/updown.go`) lacks the CSRF token validation that was added to the POST upload handler during the GHSA-jrq5-hg6x-j6g3 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). ### Details **Root Cause 1 — Missing CSRF on PUT** (`httpserver/updown.go:19`) When GHSA-jrq5-hg6x-j6g3 was fixed (commit `e3c3d37`), `checkCSRF()` was added to the POST `upload()` function (line 78) but not to the PUT `put()` function directly above it in the same file. This means PUT requests are accepted without any CSRF token. ```go // POST — protected func (fs *FileServer) upload(w http.ResponseWriter, req *http.Request) { if !fs.checkCSRF(w, req) { return } // ... } // PUT — unprotected func (fs *FileServer) put(w http.ResponseWriter, req *http.Request) { // No checkCSRF call // ... } ``` **Root Cause 2 — Wildcard CORS** (`httpserver/server.go:126`) The OPTIONS handler unconditionally returns permissive CORS headers: ```go w.Header().Set("Access-Control-Allow-Origin", "*") w.Header().Set("Access-Control-Allow-Methods", "POST, PUT, OPTIONS") w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization") ``` This allows any website's JavaScript to pass the browser's CORS preflight check and send PUT requests to the goshs server. ### PoC [poc.zip](https://github.com/user-attachments/files/26828829/poc.zip) Please extract the uploaded compressed file before proceeding 1. bash poc.sh <img width="543" height="376" alt="스크린샷 2026-04-17 오후 11 08 13" src="https://github.com/user-attachments/assets/a695cbc8-133e-4e80-a2f5-9fe9fd36b569" /> ### Impact - Arbitrary file write to the goshs webroot from any website the victim visits - File overwrite — existing files can be silently replaced

Source published

23 Apr 2026 14:28:14 UTC

Source modified

25 Jun 2026 23:11:45 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Publisher rating · MODERATE

goshs has Cross-Origin Arbitrary File Write via Missing CSRF on PUT and Wildcard CORS in github.com/patrickhener/goshs

Source published

25 Jun 2026 22:34:34 UTC

Source modified

25 Jun 2026 23:01:36 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.