CVE-2026-56735 Details
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.
A vulnerability exists in Zammad, a web-based open-source helpdesk and customer support system, in versions prior to 7.0.2 and 7.1.0. The issue arises from the HTML sanitizer, which blocks external URLs in the 'src' attribute of 'img' tags to prevent remote content loading. However, the 'srcset' attribute, also allowlisted for 'img' tags, does not undergo the same scrutiny. This oversight enables an attacker to embed arbitrary external URLs in the 'srcset' attribute by simply sending an email. When an agent views the ticket with the malicious 'srcset', the browser silently loads the attacker-controlled URL, leaking the agent's IP address, User-Agent, Referer, and the exact time the ticket was viewed. The HTML sanitizer has been updated to block external URLs in the 'srcset' attribute of 'img' tags, addressing the issue in versions 7.0.2 and 7.1.0.
Users can upgrade to Zammad versions 7.0.2 or 7.1.0 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Sep 25, 2026CISA-ADP
Assessed Sep 25, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/zammad/zammad/commit/02c1ff8dc65961352dc047013bece9dff1f2ffb7 | [email protected] | Source CodeVendor |
| https://github.com/zammad/zammad/releases/tag/7.0.2 | [email protected] | Release NotesVendor |
| https://github.com/zammad/zammad/releases/tag/7.1.0 | [email protected] | Release NotesVendor |
| https://github.com/zammad/zammad/security/advisories/GHSA-7fwx-3xr4-qm6w | [email protected] | AdvisoryRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-82 | Improper Neutralization of Script in Attributes of IMG Tags in a Web Page | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Zammad | <= 7.0.1 (semver) |
CPE
Remediation
| |
Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 25, 2026 | CVE Modified | CISA-ADP |
| Sep 25, 2026 | New CVE Received | [email protected] |