---
id: "CVE-2026-121604"
kind: "vulnerability"
aliases: ["CVE-2026-121604"]
title: "wlroots: out-of-bounds read leaks compositor heap memory via X11 window class"
severity: "medium"
cvss: 4.8
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-desktop", "runtime", "wayland", "wlroots", "xwayland"]
not_affected_if: ["no-xwayland", "wlroots-0.20.2-or-later"]
published_at: "2026-11-03T17:18:11+00:00"
first_seen_at: "2026-11-03T17:21:56+00:00"
updated_at: "2026-11-03T17:24:32+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121604", "first_seen_at": "2026-11-03T17:21:56+00:00"}]
---

# wlroots: out-of-bounds read leaks compositor heap memory via X11 window class

wlroots before 0.20.2 reads past the end of a WM_CLASS property in its Xwayland code, so a local X11 client can make the compositor expose heap bytes as a window class or app_id over IPC. The attacker gets leaked compositor memory, which may contain sensitive data.

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

## How to check

- Check the installed wlroots version: `pkg-config --modversion wlroots` or the version your compositor bundles.
- Confirm whether your compositor uses Xwayland (the xwm.c code path).

## Fix

- wlroots: move to `0.20.2` or later.

## Timeline

- 2026-11-03T17:21:56+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121604

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/wlroots-before-0.20.2-out-of-bounds-read-via-read-surface-class-in-xwm-c

## From the sources

wlroots before 0.20.2 contains an out-of-bounds read vulnerability in read_surface_class() in xwayland/xwm.c that allows local X11 clients to leak compositor heap memory. Attackers can set a WM_CLASS property with a NUL-terminated instance but unterminated class, exposing over-read heap bytes as the window class or app_id over IPC.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_