---
id: "CVE-2026-114731"
kind: "vulnerability"
aliases: ["CVE-2026-114731"]
title: "Roundcube Webmail: CSS proxy reads unlimited remote stylesheets, exhausting server memory"
severity: "medium"
cvss: 5.3
epss: 0.00431
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["mail-server", "package", "roundcube", "self-hosted"]
not_affected_if: ["patched-version"]
published_at: "2026-10-22T03:16:38+00:00"
first_seen_at: "2026-10-23T21:57:30+00:00"
updated_at: "2026-10-25T04:20:34+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-114731", "first_seen_at": "2026-10-23T21:57:30+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-114731", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Roundcube Webmail: CSS proxy reads unlimited remote stylesheets, exhausting server memory

The Roundcube CSS proxy (utils/modcss) loads a remote stylesheet fully into memory with no size limit and no read timeout. An attacker who can point a stylesheet URL at a host they control can exhaust server memory and degrade or crash the webmail service.

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

## How to check

- Check the installed version: `roundcube` version in the installation (CHANGELOG or `program/include/iniset.php` RCMAIL_VERSION)
- Confirm the CSS proxy is reachable: unknown whether it is on by default

## Fix

- Upgrade Roundcube Webmail to `1.6.20` on the 1.6 branch or `1.7.5` on the 1.7 branch
- Upstream fix: commit 'Add a size limit to the CSS proxy content processing' (5 MB cap, streamed read, read timeout)

## Timeline

- 2026-10-23T21:57:30+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-114731
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-114731

## From the sources

Roundcube Webmail before 1.6.20 and 1.7.x before 1.7.5 is affected by an uncontrolled resource consumption vulnerability in the CSS proxy (the utils/modcss action). The fetched stylesheet was read into memory in full, with no size limit and no read timeout, so a stylesheet URL referencing an attacker-controlled host could be used to exhaust server memory. Upstream fixed this in the commit “Add a size limit to the CSS proxy content processing”, which caps the response at 5 MB, reads it as a stream and applies a read timeout.

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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_