CVE-2026-26028 CryptPad: Sanitizer Bypass in Diffmarked.js Allows Arbitrary HTML Injection and Potential XSS
Attackers can inject arbitrary HTML and execute scripts in CryptPad documents by bypassing the Diffmarked.js sanitizer, compromising user sessions and data.
- 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-2026-26028?
CVE-2026-26028 is a medium-severity cross-site scripting vulnerability in cryptpad, published on 20 May 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
CryptPad is an end-to-end encrypted collaborative office suite. In versions prior to 2026.2.0, the HTML sanitizer in Diffmarked.js can be bypassed due to incomplete attribute filtering on restricted tags. The sanitizer validates only the src attribute of <iframe>, <video>, and <audio> elements, leaving all other attributes unchecked. As a result, an attacker can inject arbitrary HTML through srcdoc, completely defeating CryptPad's intended bounce sandboxing and enabling link injection or other interactive content within user-controlled documents. The root cause lies in how the sanitizer classifies and enforces tag restrictions: although it defines both forbidden and restricted tag lists, <iframe> is treated as "restricted" rather than "forbidden." Enforcement then inspects only the src attribute, so pairing a benign blob: src with a malicious srcdoc results in unrestricted rendering. This issue has been fixed in version 2026.2.0.
Which versions are affected by CVE-2026-26028?
2 open source packages ship an affected version, including cryptpad.
| Package | Affected | Fixed in |
|---|---|---|
cryptpad npm | All versions to 5.9.0 | None |
cryptpad npm | All versions to 5.9.0 | None |
How do I fix CVE-2026-26028?
No fix has been published for CVE-2026-26028 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-26028 being exploited?
There is no known exploitation of CVE-2026-26028 in the wild and no public exploit code.
Sources
Also known as GHSA-g2g4-47gv-p72v.