CVE-2026-26028
MediumWhat is CVE-2026-26028?
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.
CVSS Vector Breakdown
CVSS 3.1Exploitable remotely over the network without requiring access to the local system.
No special conditions required. Exploit can be performed reliably and repeatedly.
No authentication required. Any anonymous user can exploit this vulnerability.
Victim must take an action (e.g. click a link, open a file) for the exploit to succeed.
Exploiting the vulnerability can affect other components beyond the vulnerable one.
Some sensitive information is disclosed, but attacker has limited access.
Attacker can modify some data, but scope or consequence is limited.
No availability impact. Service remains fully operational.
FAQ
CVE-2026-26028 has a CVSS score of 6.1/10, rated as Medium. Review the affected products list and apply vendor patches.
CVSS (Common Vulnerability Scoring System) rates vulnerability severity from 0.0 to 10.0. CVE-2026-26028 scores 6.1/10 (Medium). Scores 9.0–10.0 are Critical, 7.0–8.9 are High, 4.0–6.9 are Medium, and below 4.0 are Low.
The list of devices confirmed to be affected by CVE-2026-26028 is shown in the "Affected Devices" section above. Check your firmware version against the vendor security advisory and apply the latest patch.
Apply the latest firmware or software update from the vendor. Check the References section above for official advisories and patch notes. If no patch is available, consider disabling the affected feature or isolating the device from untrusted networks.