---
id: CVE-2026-56735
title: Zammad is a web based open source helpdesk/customer support system
summary: >-
  Zammad is a web based open source helpdesk/customer support system. Prior to
  7.0.2 and 7.1.0, zammad's HTML sanitizer (HtmlSanitizer::Strict) blocks
  external URLs in  to prevent remote content loading, but the srcset attribute,
  also allo…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N'
cwe:
  - CWE-82
vendor: zammad
product: zammad
affected:
  - zammad < 7.0.2
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T19:17:43.023'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-56735'
references:
  - url: >-
      https://github.com/zammad/zammad/commit/02c1ff8dc65961352dc047013bece9dff1f2ffb7
    label: security-advisories@github.com
  - url: 'https://github.com/zammad/zammad/releases/tag/7.0.2'
    label: security-advisories@github.com
  - url: 'https://github.com/zammad/zammad/releases/tag/7.1.0'
    label: security-advisories@github.com
  - url: 'https://github.com/zammad/zammad/security/advisories/GHSA-7fwx-3xr4-qm6w'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-25T19:06:28.516570Z'
cvssSource: cna
ingestedAt: '2026-09-25T18:14:20.465Z'
epss: 0.00421
epssPercentile: 0.33915
---

## Overview

Zammad is a web based open source helpdesk/customer support system. Prior to 7.0.2 and 7.1.0, zammad's HTML sanitizer (HtmlSanitizer::Strict) blocks external URLs in  to prevent remote content loading, but the srcset attribute, also allowlisted for , is not subject to the same check. This oversight allows an attacker to embed arbitrary external URLs in the srcset attribute just by sending an e-mail, effectively bypassing the external content protection. When an agent views the ticket containing the malicious srcset, the browser will silently load the attacker-controlled URL, resulting in the leakage of the agent's IP address, User-Agent, Referer, and the exact time the ticket was viewed. HtmlSanitizer::Strict got extended to block external URLs in the srcset attribute of  tags. This was done to prevent tracking pixels and external content loading, which could compromise user privacy. This issue is fixed in versions 7.0.2 and 7.1.0.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.