# 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.

- **Severity:** Medium 5.3 (`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`)
- **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 available:** No
- **Published:** 25 Sep 2026
- **Updated:** 25 Sep 2026
- **Also known as:** GHSA-7fwx-3xr4-qm6w

## 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 (Improper Neutralization of Script in Attributes of IMG Tags in a Web Page)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56735 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-56735 in the wild and no public exploit code.

Affected product: zammad. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56735/ (Markdown: https://insights.sbomify.com/CVE-2026-56735/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56735
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56735
- OSV: https://osv.dev/vulnerability/CVE-2026-56735

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-56735/
Summaries are generated and may contain mistakes; the official description above is the record.