Is CVE-2026-56735 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-56735 being exploited in the wild.

How severe is CVE-2026-56735?

Informational severity, published 25 September 2026.

Which products and versions are affected?

Zammad prior to 7.0.2 and 7.1.0.

Is there a fix for CVE-2026-56735?

A patch was published on 2026-06-15. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-56735 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-56735?

Check whether you run Zammad at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-56735: Zammad HTML sanitizer bypass via srcset attribute

CVE-2026-56735 · Severity: info · Published 2026-09-25

Zammad's helpdesk system filters harmful content in customer emails to prevent malicious code execution. However, a flaw in its HTML sanitizer allows attackers to bypass this protection by embedding tracking pixels or external URLs in image srcset attributes. When support agents view a ticket containing such a malicious email, their browser automatically loads the attacker-controlled URL, leaking their IP address, browser details, and the exact time they viewed the ticket—enabling privacy compromise and potential phishing attacks.

Technologies: Zammad. Vendors: Zammad.

Quick answers

Is CVE-2026-56735 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-56735 being exploited in the wild.
How severe is CVE-2026-56735?: Informational severity, published 25 September 2026.
Which products and versions are affected?: Zammad prior to 7.0.2 and 7.1.0.
Is there a fix for CVE-2026-56735?: A patch was published on 2026-06-15. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-56735 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-56735?: Check whether you run Zammad at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The HtmlSanitizer::Strict class blocks external URLs in img src attributes but failed to apply the same restriction to the srcset attribute, which is also allowlisted for img tags. An attacker can send an email with a crafted srcset containing external URLs; when an agent views the ticket in Zammad's web interface, the browser silently fetches these resources, leaking sensitive metadata (IP, User-Agent, Referer, timestamp). The vulnerability exists in versions prior to 7.0.2 and 7.1.0 and is fixed by extending the sanitizer to remove unsafe srcset entries.

Affected products

Zammad Zammad prior to 7.0.2 and 7.1.0

Timeline

2026-09-25: disclosed
2026-06-15: patched

References

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