---
id: "CVE-2026-128021"
page: "https://infrastack.ai/live/CVE-2026-128021"
kind: "vulnerability"
aliases: ["CVE-2026-128021"]
title: "FrankenPHP: libxml errors leak between clients in worker mode"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["frankenphp", "libxml", "php", "runtime", "worker-mode"]
not_affected_if: ["default-config", "non-worker-mode"]
published_at: "2026-11-13T10:18:07+00:00"
first_seen_at: "2026-11-13T10:47:31+00:00"
updated_at: "2026-11-13T10:55:13+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-128021", "first_seen_at": "2026-11-13T10:47:31+00:00"}]
exploit_sources: []
---

# FrankenPHP: libxml errors leak between clients in worker mode

Link for people: https://infrastack.ai/live/CVE-2026-128021 (this .md is for agents)

FrankenPHP before 1.13.2 never clears libxml error state between requests in worker mode, so a later client can read earlier clients' libxml errors. An attacker can get other clients' parsed-document fragments and server filesystem paths.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `frankenphp version` shows the installed version; below `1.13.2` is affected
- Check whether worker mode is enabled in the FrankenPHP or Caddy configuration, since the flaw is in worker mode
- Check whether the application calls libxml parsing on untrusted input

## Fix

- FrankenPHP: move to `1.13.2` or later

## Timeline

- 2026-11-13T10:47:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-128021

## Documents

- [advisory] Vendor advisory: github.com https://github.com/php/frankenphp/security/advisories/GHSA-4gfw-9v29-gp9h
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/frankenphp-before-1.13.2-information-disclosure-via-libxml-error-state-in-worker-mode

## From the sources

FrankenPHP before 1.13.2 contains an information disclosure vulnerability that allows later clients to read earlier clients' libxml errors because worker mode never resets LIBXML(error_list) between requests. Attackers sending requests to the same worker thread can call libxml_get_errors() or libxml_get_last_error() to obtain other clients' parsed-document fragments and server filesystem paths.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_