CVE-2026-104252: Vitess vttablet /twopcz reflected XSS

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.9%, percentile 59: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 59% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes vitess.io/vitess (Go) < 0.23.5, fixed in 0.23.5; vitess.io/vitess (Go) >= 0.24.0, < 0.24.2, fixed in 0.24.2. Check your lockfile, including transitive dependencies.

What it is

Vitess is a database clustering system for horizontal scaling of MySQL. Prior to 23.0.5 and 24.0.2, twopczHandler in go/vt/vttablet/tabletserver/twopcz.go writes the Action and dtid form values from the vttablet and vtcombo /twopcz HTTP debug endpoint into a text/html response without HTML escaping. Under the default allow-all ACL policy, a remote unauthenticated attacker can send an operator a crafted request that executes script in the operator's browser after the request is opened. The script runs with the vttablet debug origin and can read same-origin diagnostic endpoints that expose query, transaction, environment, variable, or profiling data available in that deployment. This issue is fixed in versions 23.0.5 and 24.0.2.

From the GitHub advisory

From: xylove21 To: security@vitess.io Subject: [Security Report] Vitess vttablet /twopcz reflected XSS Date: Tue, 24 Jun 2026 14:30:00 +0800

Summary

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).

Weakness type: CWE-79, CWE-80, CWE-116.

Product: vitess.io/vitess (Go) · Assigned by: GitHub_M · Published: 2026-10-13

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.89% probability of exploitation activity in the next 30 days; percentile 59.

Timeline

• 2026-10-13 — CVE record published by GitHub_M
• 2026-10-15 — CVE record last updated
• 2026-10-15 — GitHub-reviewed advisory GHSA-v75v-6fpf-gvw8 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-v75v-6fpf-gvw8 github.com
2. CVE.org record CVE-2026-104252 cve.org
3. NVD entry CVE-2026-104252 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
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3. github.com github.com
4. github.com github.com
5. github.com github.com
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7. github.com github.com
8. github.com github.com
9. github.com github.com

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