| Package | Affected versions | Patched versions |
|---|---|---|
| vitess.io/vitess | ≥ 0.24.0, < 0.24.2< 0.23.5 | 0.24.20.23.5 |
| vitess | ≥ 24.0.0, < 24.0.2< 23.0.5 | 24.0.223.0.5 |
From: xylove21 To: [email protected] Subject: [Security Report] Vitess vttablet /twopcz reflected XSS Date: Tue, 24 Jun 2026 14:30:00 +0800
The twopczHandler in
go/vt/vttablet/tabletserver/twopcz.go (line 185) reflects the Action
and dtid form values directly into the HTML response body via
fmt.Fprintln(w, msg) — without HTML escaping. The response is served
as text/html; charset=utf-8, and Vitess's default acl policy is
allow-all, so the endpoint is reachable by anyone who can hit the
vttablet's HTTP port (default 15999, multiplexed with gRPC and MySQL
wire-protocol ports).
A crafted Action or dtid value yields a reflected XSS that
executes in the operator's browser with same-origin access to the
vttablet's debug endpoints. This includes /queryz (live query plans),
/querylogz (recent queries with bound values), /txlogz (transactions),
/debug/env (environment variables — may include MySQL/topology
credentials), /debug/vars (expvar stats), and /debug/pprof/* if
enabled.
The bug was introduced before v20.0.0 (long-standing) and was silently
fixed in commit 3140c1846c (merged 2026-06-09, PR #20255,
"tabletserver: escape reflected form values in twopcz handler"). The
fix replaces fmt.Fprintln(w, msg) with
fmt.Fprintln(w, html.EscapeString(msg)). No released version of
Vitess contains the fix — the fix lives only on main (current tip
33a3c0fafe69, 2026-06-23). There is no CVE, GHSA, or OSV entry
for this specific bug (verified 2026-06-24 against GitHub Advisory
Database, OSV.dev, and NVD).
| Field | Value |
|---|---|
| Type | Reflected Cross-Site Scripting (XSS) |
| CVSS 3.1 | AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N = 7.7 HIGH |
| Attack Vector | Network (vttablet HTTP port 15999, multiplexed with gRPC/MySQL) |
| Attack Complexity | Low (craft URL, send to operator) |
| Privileges Required | None (default acl policy is allow-all) |
| User Interaction | Required (operator must visit crafted URL) |
| Scope | Changed (XSS chain reaction to other vttablet debug endpoints) |
| Confidentiality | High (query text, env vars, expvar stats) |
| Integrity | None (XSS itself doesn't change state) |
| Availability | None (XSS itself doesn't disrupt service) |
All released versions are vulnerable. The fix lives only on main:
| Tag | Released | twopcz.go line 185 | Status |
|---|---|---|---|
| v20.0.0 | 2024-06-27 | fmt.Fprintln(w, msg) | BUGGY |
| v20.0.1 - v20.0.6 | 2024 | fmt.Fprintln(w, msg) | BUGGY |
| v22.0.4 | 2026-02-27 | fmt.Fprintln(w, msg) | BUGGY |
| v23.0.3, v23.0.4 | 2026-02 / 2026-05 | fmt.Fprintln(w, msg) | BUGGY |
| v24.0.0, v24.0.1 | 2026-04 / 2026-05 | fmt.Fprintln(w, msg) | BUGGY |
main (33a3c0fafe69) | 2026-06-23 | fmt.Fprintln(w, html.EscapeString(msg)) | FIXED |
A successful XSS lands in the vttablet's origin. From there, the
attacker can fetch (via fetch() from injected JavaScript) the
following same-origin endpoints, all of which are unauthenticated by
default:
/twopcz — in-flight 2PC transactions (query text, parameters, dtid)/queryz — live query plans/querylogz — recent queries with bound values/txlogz — transactions/debug/env — environment variables (may include MySQL creds, topology
credentials, encryption keys)/debug/vars — expvar stats/debug/pprof/* — CPU/memory profiles (if enabled)The PoC is a self-contained Go HTTP server that replicates the buggy
twopczHandler from Vitess v20.0.0 verbatim (using the same line-185
code). It runs on 127.0.0.1:15080 and returns the same response shape
as the real Vitess endpoint.
# 1) Build the PoC (Go 1.23+)
cd /path/to/finding/CVE-pending-twopcz-xss
go build -o /tmp/vitess-twopcz-poc ./poc.go
# 2) Start the buggy server
ADDR=127.0.0.1:15080 /tmp/vitess-twopcz-poc &
# 3) Reproduce — Test 1: bare GET (no params)
curl -sS -i "http://127.0.0.1:15080/twopcz"
# → Content-Type: text/html; charset=utf-8, status 200
# 4) Test 2: XSS via Action param (URL-encode the script tag)
curl -sS -i "http://127.0.0.1:15080/twopcz?Action=%3Cscript%3Ealert(1)%3C%2Fscript%3E&dtid=zz"
# → Response body contains literal "<script>alert(1)</script>(zz): completed."
# → Browser executes the script as same-origin code
# 5) Test 3: XSS via dtid param (attribute-context payload)
curl -sS -i "http://127.0.0.1:15080/twopcz?Action=Demo&dtid=%3Cimg%20src%3Dx%20onerror%3Dalert(1)%3E"
# → Response body contains literal "<img src=x onerror=alert(1)>"
# → Browser fires the onerror handler as same-origin code
# 6) Run the 3x automated runner (writes evidence/run-{1,2,3}.log)
bash ./poc/run.sh
PoC result excerpt (from evidence/run-1.log):
--- Test 2: XSS via Action=<script>alert(1)</script> ---
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
...
<h2>WARNING: Actions on this page can jeopardize data integrity.</h2>
<script>alert(1)</script>(zz): completed.
PASS: payload reflected UNESCAPED (XSS exploitable in browser)
The PoC was run 3 times on the buggy server (all 3/3 PASS) and the same
code is byte-identical to the v20.0.0 commit 8aeb274f6c8e line 185.
go/vt/vttablet/tabletserver/twopcz.go (v20.0.0 through v24.0.1):
// Line 185
fmt.Fprintln(w, msg)
msg is constructed earlier in the handler as:
msg := fmt.Sprintf("%s(%s): completed.", action, dtid)
with action and dtid coming from the form values
r.FormValue("Action") and r.FormValue("dtid"). The form values are
URL-decoded (so a + becomes a space, %3C becomes <) but never
HTML-escaped. The handler explicitly sets Content-Type: text/html; charset=utf-8 (via the <!DOCTYPE html> it writes first), so the
browser executes any injected <script> or attribute-context payload.
The fix in main (fmt.Fprintln(w, html.EscapeString(msg))) closes the
hole by HTML-escaping both action and dtid before reflection.
// Recommended minimal patch (already in main, needs backport to all release branches):
import "html"
func twopczHandler(w http.ResponseWriter, r *http.Request) {
// ... existing logic ...
msg := fmt.Sprintf("%s(%s): completed.", action, dtid)
fmt.Fprintln(w, html.EscapeString(msg)) // ← was: fmt.Fprintln(w, msg)
}
Backport the fix to v20.0.x, v22.0.x, v23.0.x, and v24.0.x as patch
releases. The fix is one line and a one-line import "html" addition,
so the backport risk is minimal.
If you cannot upgrade to a fixed release immediately:
Restrict the vttablet HTTP port (default 15999) to localhost
only. vttablet can run with --tablet-allow-stats=false and
--tablet-grpc-port configured separately from the HTTP port, or
you can firewall the HTTP port at the network layer. The debug
endpoints are not needed by production traffic.
Set a non-default ACL policy. Vitess supports an acl policy
that defaults to allow-all. Setting it to a JSON file that denies
unauthenticated access to debug endpoints (see
go/acl/acl.go::savePolicy) would block the XSS, but the default
policy is currently "" (allow-all) and many users don't override
it.
Use a reverse proxy (nginx, envoy) in front of the vttablet HTTP port with a strict allowlist of clients.
/debug/querylogz HTML injection, fixed in
v20.0.4 — different endpoint)Running one of these products? Scan your site to see whether it exposes a vulnerable version.
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