CVE-2026-56735

Zammad: Improper neutralization of `srcset` attribute in IMG tags in Zammad

Published Sep 25, 2026 CVSS 4.0 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
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

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Zammad
Zammad zammad
Vendors & Products Zammad
Zammad zammad
Type Values Removed Values Added
Description 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.
Title Zammad: Improper neutralization of `srcset` attribute in IMG tags in Zammad
Weaknesses CWE-82
References
Metrics cvssV4_0

{'score': 5.3, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 25, 2026, 7:06 PM
Reserved
Jun 22, 2026, 7:17 PM
Status
Deferred
Published
Sep 25, 2026, 6:17 PM
Modified
Sep 28, 2026, 2:45 PM