CVE-2026-56735 Zammad: Improper neutralization of `srcset` attribute in IMG tags in Zammad
Attackers can leak agent IP, User-Agent, and viewing time by embedding external URLs in srcset attributes within ticket emails.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-56735?
CVE-2026-56735 is a medium-severity vulnerability in zammad, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-82
Which versions are affected by CVE-2026-56735?
How do I fix CVE-2026-56735?
No fix has been published for CVE-2026-56735 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-56735 being exploited?
There is no known exploitation of CVE-2026-56735 in the wild and no public exploit code.
Sources
Also known as GHSA-7fwx-3xr4-qm6w.