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CVE-2026-56735— Zammad: Improper neutralization of `srcset` attribute in IMG tags in Zammad

Quick assessment

Affected
zammad zammad
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Zammad 是一款基于 Web 的开源帮助中心/客户支持系统。在 7.0.2 和 7.1.0 版本之前，Zammad 的 HTML sanitizers（HtmlSanitizer::Strict）会阻止 标签中的外部 URL，以防止远程内容加载；然而，同时被列入允许列表（allowlisted）的 属性并未受到相同的检查。这一疏忽使得攻击者只需发送一封电子邮件，即可在 标签的 属性中嵌入任意外部 URL，从而有效绕过外部内容防护机制。当客服人员查看包含恶意 的工单时，浏览器将静默加载攻击者控制的 URL，导致客

CVSS 5.3 · Medium EPSS 0.42% · P34
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I. Basic Information for CVE-2026-56735

Vulnerability Information
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Vulnerability Title
Zammad: Improper neutralization of `srcset` attribute in IMG tags in Zammad
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
Web页面IMG标签属性中脚本转义处理不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
zammad zammad < 7.0.2 -

II. Public POCs for CVE-2026-56735

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III. Intelligence Information for CVE-2026-56735

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Other References for CVE-2026-56735 (4)

Same Patch Batch · zammad · 2026-09-25 · 30 CVEs total

CVE-2026-84458 9.1 CRITICAL Zammad: Account takeover via unverified email matching during SSO auto-link
CVE-2026-61525 8.8 HIGH Zammad: Arbitrary File Deletion via Unvalidated Session Identifier in Long Polling Control
CVE-2026-56733 8.7 HIGH Zammad: Incorrect Authorization and Improper Privilege Management
CVE-2026-56725 8.7 HIGH Zammad: Denial of Service via OTRS Import Controller
CVE-2026-84462 8.6 HIGH Zammad: AI Agent template sanitizer bypass leads to remote code execution
CVE-2026-56731 8.4 HIGH Zammad: Cross-Site Scripting in Ticket Notifications
CVE-2026-56724 7.1 HIGH Zammad: Incorrect implementation of permission checks in the knowledge base module
CVE-2026-84465 7.1 HIGH Zammad: S/MIME signature verification allows forged sender impersonation
CVE-2026-84464 7.1 HIGH Zammad: IDOR in External Data Source rendering exposes ticket, user, group, and organizati
CVE-2026-56727 7.1 HIGH Zammad: PGP signature spoofing via unvalidated verification return
CVE-2026-56723 7.1 HIGH Zammad: Missing authorization on ticket attachment download
CVE-2026-84461 6.9 MEDIUM Zammad: Missing rate limiting allows password brute-forcing during two-factor login
CVE-2026-63207 6.9 MEDIUM Zammad: Sensitive Information Exposure in Integration Administration API
CVE-2026-84463 6.3 MEDIUM Zammad: Stored HTML injection in Knowledge Base video widget enables forced session switch
CVE-2026-56728 5.3 MEDIUM Zammad: Cross-User Taskbar Item Access Control Vulnerability
CVE-2026-63206 5.3 MEDIUM Zammad: Remote image tracking bypass via shortened URL scheme
CVE-2026-56734 5.3 MEDIUM Zammad: Avatar Image URL Server-Side Request Forwarding
CVE-2026-56732 5.3 MEDIUM Zammad: Malicious input in Ticket Body Enables Session Termination
CVE-2026-84460 5.3 MEDIUM Zammad: Missing Authorization in TagsController#list Allows Cross-Object Tag Enumeration
CVE-2026-61855 5.3 MEDIUM Zammad: Invalid PGP Detached Signatures Reported as Good Signature on Inbound Mail

Showing top 20 of 30 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: zammad
Same vendor: zammad
Same weakness: CWE-82

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