CVE-2026-26028: Cryptpad Cross-Site Scripting Vulnerability
MODERATECVE-2026-26028 is a MODERATE (CVSS 6.1) cross-site scripting vulnerability (CWE-116: Improper Encoding or Escaping of Output) affecting Cryptpad libraries in the npm ecosystem. The issue involves cryptpad has a sanitizer bypass in diffmarked.js that allows arbitrary html injection and potential xss. Remediation is available in the latest vendor maintenance releases.
CVE-2026-26028 at a Glance
Security Impact
CVSS: 6.1
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).
How to Fix CVE-2026-26028
To remediate this vulnerability, upgrade all affected Cryptpad dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install cryptpad@Latest secure releaseRun the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls cryptpadHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-26028, inspect your project dependencies using npm:
npm ls cryptpadAnalyze the terminal output to locate any version of Cryptpad in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.
Note: The npm ls cryptpad command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-116: Improper Encoding or Escaping of Output, where the product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. as a result, the intended structure of the message is not preserved. In Cryptpad, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-26028 Affected Cryptpad Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
cryptpad
|
npm |
≤ 5.9.0
|
|
References
Frequently Asked Questions
What is CVE-2026-26028?
Which Cryptpad versions are affected?
What version fixes CVE-2026-26028?
Is cryptpad affected?
What is the CVSS score of CVE-2026-26028?
What CWE is associated with CVE-2026-26028?
How can I check npm dependencies for CVE-2026-26028?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-g2g4-47gv-p72v",
"modified" : "2026-05-26T19:05:10Z",
"published" : "2026-05-26T19:05:10Z",
"aliases" : [ "CVE-2026-26028" ],
"summary" : "CryptPad has a Sanitizer Bypass in Diffmarked.js that Allows Arbitrary HTML Injection and Potential XSS",
"details" : "### Summary\nCryptPad’s HTML sanitizer in Diffmarked.js can be bypassed due to incomplete filtering of restricted tags.\nBecause the sanitizer only validates the src attribute of `<iframe>` `<video>`, and `<audio>` elements, and does not restrict other attributes, an attacker can inject arbitrary HTML through srcdoc. This completely defeats CryptPad’s intended bounce sandboxing and allows link injection or other interactive content inside user-controlled documents.\n\n### Details\nThe sanitizer defines forbidden and restricted tags but treats <iframe> as “restricted” instead of “forbidden”:\n\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L403-L407\nThe actual enforcement only checks the src attribute, nothing else:\n\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L445-L449\n\nBecause only src is validated, adding a benign blob: src but malicious srcdoc results in unrestricted rendering.\n### PoC\n\nAn attacker can embed arbitrary HTML, including clickable external links, images, or interactive content, completely bypassing CryptPad’s bounce mechanism and sanitization:\n\n```html\n<iframe src=blob: srcdoc=\"<a href=https://attacker.com target=_blank>CLICK ME</a>\"></iframe>\n```\n\nAlthough CSP is strict, CryptPad exposes several same-origin gadgets that can execute attacker-controlled code.\n\nFor example, `jscolor.js` dynamically evaluates user-provided options:\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/jscolor.js#L65-L71\n\n### Impact\nSanitizer bypass, HTML injection and potentially XSS.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "cryptpad"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"last_affected" : "5.9.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/cryptpad/cryptpad/security/advisories/GHSA-g2g4-47gv-p72v"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26028"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/cryptpad/cryptpad"
}, {
"type" : "WEB",
"url" : "https://github.com/cryptpad/cryptpad/releases/tag/2026.2.0"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-116", "CWE-79" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-05-26T19:05:10Z",
"nvd_published_at" : "2026-05-20T20:16:36Z"
}
}