{"id":"CVE-2026-26028","aliases":["EUVD-2026-31154","GHSA-g2g4-47gv-p72v"],"status":"published","title":"CryptPad: Sanitizer Bypass in Diffmarked.js Allows Arbitrary HTML Injection and Potential XSS","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 \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e 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, \u003ciframe\u003e 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.","severity":{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00242,"percentile":0.15507,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-116","CWE-79"],"published":"2026-05-20T18:51:43Z","modified":"2026-10-28T02:31:11Z","affected":[{"source":"ghsa","ecosystem":"npm","package":"cryptpad","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"5.9.0"}]}]},{"source":"osv","ecosystem":"npm","package":"cryptpad","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"last_affected":"5.9.0"}]}]}],"products":[{"vendor":"cryptpad","product":"cryptpad"}],"references":[{"url":"https://github.com/cryptpad/cryptpad/security/advisories/GHSA-g2g4-47gv-p72v","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/cryptpad/cryptpad/releases/tag/2026.2.0","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-26028","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-g2g4-47gv-p72v"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/26xxx/CVE-2026-26028.json","tags":["advisory"]},{"url":"https://github.com/cryptpad/cryptpad","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-26028","title":"CryptPad: Sanitizer Bypass in Diffmarked.js Allows Arbitrary HTML Injection and Potential XSS","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 \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e 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, \u003ciframe\u003e 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.","status":"published","published":"2026-05-20T18:51:43.643Z","modified":"2026-05-20T19:33:12.902Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-116","CWE-79"],"updated_at":"2026-11-02T13:38:20.971157Z"}],"euvd":[{"id":"EUVD-2026-31154","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 \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e 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, \u003ciframe\u003e 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.","status":"published","published":"2026-05-20T18:51:43Z","modified":"2026-05-20T19:33:12Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T18:21:13.845677Z"}],"ghsa":[{"id":"GHSA-g2g4-47gv-p72v","title":"CryptPad has a Sanitizer Bypass in Diffmarked.js that Allows Arbitrary HTML Injection and Potential XSS","description":"### 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 `\u003ciframe\u003e` `\u003cvideo\u003e`, and `\u003caudio\u003e` 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 \u003ciframe\u003e 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\u003ciframe src=blob: srcdoc=\"\u003ca href=https://attacker.com target=_blank\u003eCLICK ME\u003c/a\u003e\"\u003e\u003c/iframe\u003e\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.","status":"published","published":"2026-05-26T19:05:10Z","modified":"2026-05-26T19:05:11Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-79","CWE-116"],"updated_at":"2026-11-02T14:40:13.628377Z"}],"nvd":[{"id":"CVE-2026-26028","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 \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e 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, \u003ciframe\u003e 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.","status":"published","published":"2026-05-20T20:16:36.76Z","modified":"2026-07-23T12:10:00.11Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-79","CWE-116"],"updated_at":"2026-11-02T14:12:19.752984Z"}],"osv":[{"id":"CVE-2026-26028","title":"CryptPad: Sanitizer Bypass in Diffmarked.js Allows Arbitrary HTML Injection and Potential XSS","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 \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e 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, \u003ciframe\u003e 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.","status":"published","published":"2026-05-20T18:51:43.643Z","modified":"2026-10-28T02:31:11.515643195Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-116","CWE-79"],"updated_at":"2026-11-02T15:44:59.80315Z"},{"id":"GHSA-g2g4-47gv-p72v","title":"CryptPad has a Sanitizer Bypass in Diffmarked.js that Allows Arbitrary HTML Injection and Potential XSS","description":"### 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 `\u003ciframe\u003e` `\u003cvideo\u003e`, and `\u003caudio\u003e` 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 \u003ciframe\u003e 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\u003ciframe src=blob: srcdoc=\"\u003ca href=https://attacker.com target=_blank\u003eCLICK ME\u003c/a\u003e\"\u003e\u003c/iframe\u003e\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.","status":"published","published":"2026-05-26T19:05:10Z","modified":"2026-06-09T05:15:08.331432487Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-116","CWE-79"],"updated_at":"2026-11-02T15:46:47.119724Z"}]}}